Tbi swap build thread
 

I am going to atemped my first build thread for who ever wanted to swap in a 87-94 STOCK TBI SYSTEM. I am going to use the intake (& all the hardware),throtlebody,stock wiring harness and all the other things you need to do this swap. I am going to go pin by pin, wire by wire ,and tell you where everything goes.
I know this is a common swap now a days but when I started looking for info for this swap i had do go and find info from alot of deferant web sites. I would like for people that are intrested in doing this swap when they google "tbi swap" they come to this site (67-72chevytrucks.com). So here we go.

Here are some pics of my truck and motor.

The motor is a 90 model 350 tbi motor. I swaped this motor in last year and i used it because I had plans on doing this very swap then. The reason I did not do the tbi swap then was because this truck came stock with a 4.3 in it. I did not want to swap a deferent motor and try to swap the truck to tbi at the same time. So I rebuilt this motor and bouhgt a eldebrok carb intake for tbi heads and used a quadrajet.

I will have some more pics tomarow so stay tuned.

Re: Tbi swap build thread
 

Ok here we go I got all the pins labeled today was able to take two pics before the camera batt's played out (got new ones tonite), will show the labeled harness tomarow. Here are the two I got off today. It's the engine after I striped all the top-end off. I am rather proud of how clean my rebuilt engine is after a year of daily driving (and a little off road stuff).

Re: Tbi swap build thread
 

Ok here are all the pin outs and the color of the wires. My computer is the standard #1227747

A1- grn/wht- this wire is used to power the fuel pump-relay.
A2- no wire
A3- no wire
A4- gry- to egr-relay. This is a ground for the ECM to control the EGR relay.
A5- brn/wht- service soon light. This is a ground to turn on the light.
A6- pink/blk- switched 12v from the ignition relay.
A7- no wire
A8- ornange aldl serial data wire pin-e
A9- wht/blk-aldl pin B When jumpered to ground will set the computer to diagnostic mode.
A10- brn- VSS speed sensor signal to the computer, (This wire I will wire this to on side of a after market VSS sensor and the other wire on the sensor goes to ground).
A11- blk- MAP sensor ground.
A12- blk/wht- System ground. This wire is tied to other grounds in the harness and goes to engine ground.

B1- orn- 12v batt power ( I looked and traced down this wire on my 87 cab harness and this is fuesed I think it was a 15). I will probably use a inline fuse.
B2- tan/wht- Fuel pump signal from the relay. This one ties into several places, the fuel pump, the relay, and the ecm. When the relay is on it sends 12 volts to trun on the fuel pump.
B3- blk/red- Distributor plug
B4- no wire
B5- purple/wht- Distributor plug
B6- no wire
B7- blk- ESC signal This is the knock sensor signal to the computer.
B8- dk grn- AC signal. This tells the ECM that the AC is turned on. I am going to tie this into the ac clutch wire.
B9- no wire
B10-orange/blk- park neutral switch wire. some people say this is optional but I do not think it is because it gives a signal to the computer to give the engine a slight bump in rpm.(if you don't need it why did they put it there?)
B11- no wire
B12- no wire

C1- no wire
C2- brn- wire is not needed
C3-grn/blk- Idle air control
C4-grn/wht- Idle air control
C5-blue/wht- Idle air control
C6-blue/blk- Idle air control C3-C6 all go to the Idle air control valve plug on the TBI it's self.
C7- no wire
C8- no wire
C9- purple/wht-Starter crank signal wire. Goes to the small terminal of the starter.
C10- yel- Temp sender
C11- lt grn- Map sensor
C12- no wire
C13- dk blu- throtle position sensor
C14- gry- signal to map and TPS. ( you will see it tied together in the harness)
C15- on wire
C16- orange- This wire is tied with B1 so it is a 12volt wire

D1- brn/wht- system ground goes to the engine.
D2- blk- tied to the wires for the engine ground.
D3- no wire
D4- wht- distrbutor plug
D5- tan/blk- distrbutor bypass. This is the wire that you disconnect to set your timing.
D6- Tan- O2 sensor ground to engine.
D7- purple- plugs in to the o2 sensor
D8- D13 no wire
D14- grn- Injector plug plugs into the top of injector
D15- no wire
D16- blue- Injector plug plugs into the other injector

Re: Tbi swap build thread
 

The harness I am using came from a 87 truck (thanks beater c-10), I also had a 90 suburban I bought for parts and I have that harness also to save for anouther project. Anyway I will show everybody tomarow where the stock suburban harness came out of the truck. It is in the same location on this 86 truck because it had the esc distribitor from the factory. I am going to use this hole.( It's on the pass side also)

I looked at a 92 today and they would probably have a little extra wire if you use that harness but not so much that you could not make it look factory if you wanted to. :chevy:

Re: Tbi swap build thread
 

I have the stock 700 in it. I will probablly hook the cruise up later down the road but not this time. And I am going to use a vss sensor from jag that run.
Stay tuned.

Re: Tbi swap build thread
 

Part numbers of interest
Part Description Part #
TBI ECM 1227747 BCC ASDU: 1227747
Heated O-Sensor 4-wire: 25312184; AFS75
TBI Overhall Kit: CK1081
Injectors (350) Orange Black: 17112493; 217-344; 5235206
Coolant Temperature Sensor (CTS): 12146312; 25036979
Throttle Position Sensor (TPS): 12116257; 17111787; 17111471
Manifold Absolute Pressure (MAP): 16137039; 2131545; 16017460; PS10076
Idle Air Control Valve (IAC): 17111460; 25527077; AC102
EGR Control Solenoid: 1997111?; EVS30; 17112193
VSS (from JTR): 2PRS
Knock Sensor (350): 10456288; SU154
Engine Spark Control Module (ESC): 16128261; 16131231

Re: Tbi swap build thread
 

Well I did not get to my truck till late today. But I did get rid of all the wires I do not need on the harness. What you see in the first pic is the harness all labeled and sorted out. As you can see it is kind of in two parts. Tomarrow I am going to take apart all the tie points in the harness and that will untangle the last of the wires and then i will recrimp all the tie points like the factory but hopefully a little less of a spaghetti mess. I will take pics of before and after i do this.

The second pic is where i am going to run my wires in the cab. It is the rubber grommet for the esc brain. It is the same size hole that was in the 90 suburban, so it should work real nice.

In the third pic you see the factory oil presure unit and switch adapter, in the last pic is the one out of the suburban that I will have to use because the tbi oil switch adapter has a different thread size than the carb model. I think I will just drill and tap the 90 model adapter for for the stock gage sending unit. You have to use this stock tbi switch to tell the ecm that the engine has oil press. because the fuel pump wire is run through this switch.

I will try and post here again tomarow. stay tuned.

Re: Tbi swap build thread
 

You may want to temporarily drop dizzy back in to check for interference between dizzy body and oil pressure switch. I have a spare SB sitting on engine stand - this gave me ample opportunity to check interference.

Re: Tbi swap build thread
 

If you use in tank pumps you will have to get a FI tank. The fuel injected tanks have baffels in them to control fuel slosh so the pump will not suck air if the tank is low of gas. Plus you will have to get the sending unit and pump.

I am just going with one tank right now because that is what i have. I will get both tanks working in the futrue.

I have talked with "Dirtylarry" about what he did and it sounds real good.

He swap the one primary tank on his truck with the in tank pump, and then monted a transfer pump so he can just pump gas out of the spare tank when he needs it. It will be cheaper I think than making every thing work like stock. (unless I can find a donor parts truck cheap)

Re: Tbi swap build thread
 

Well I got to work on the old truck today. Got a little done before I had to quit.

First I untangeled the harness a litle more. I cut all the tie points on the harness and re soldered them so they are all untangeled, and i can route the harness some time this week hopefully. THe first pic is what you will find with a stock tbi harness with all the tie points. They are crimped and covered with tape from the factory. The pic has a sample of both.

Second I got the oil sending unit and switch fixed. I went to the parts store and got an brass adapter to adapt my oil switch to the tee threads. Problem sloved.

Third I instaled the intake on the motor I to use anouther intake than the one in the pic above because I found a crack in on of the back bolt holes. So I was thankfull that I had a spare. You can see in the last pic of the oil switch and sending unit instaled on the block. Stay tuned.

Re: Tbi swap build thread
 

My truck has dual tanks but I only use one so I guess it doesn`t matter. I`ve only used the other tank when I was running low on gas and was worried if I had enough to get to the station.

Re: Tbi swap build thread
 

This is going to be a nice and informative thread!

With TBI, I think you guys will probably be fine running a frame mounted pump to pull fuel through the dual tank switch valve however you may need to figure out a way to pause the frame mounted pump while you switch tanks otherwise you will stumble the engine momentarily. As far as the pump, just mount the pump as low as you can below the tanks and switch valve and on the engine side of the switch valve.

The problem I had running a frame mounted pump with my 8.1L was twofold. First, 8.1L requires 60 psi fuel pressure but on my marine controlled 8.1L it only requires 43 psi. None the less, the return side ports on the OEM switch valve are little bitty 5/16 ports and restrict the high pressure fuel return flow back to the tank causing the fuel pressure to run around 100 psi at the fuel rail! Once I bypassed the switch valve the fuel pressure ran normal. This would not be an issue for TBI as TBI only runs around 12 psi and what little fuel goes back to the tank is very small compared the later model sequential EFI engines. GM used that exact switch valve on TBI trucks anyway so again, the fuel return through the switch valve won't be a problem.

The second issue I had with the frame mounted pump was mainly off-road where you are crawling along on the trails at 2 MPH for hours on end without any wind blowing over the pump to keep it cool. Once I would stop for a minute to take break or something then try to restart the truck it would only crank as the fuel pump was too hot and cavitated the fuel inside. The pump would scream like crazy when it was warm too! Being my truck sees more off-road than on, I wasn’t going to be able to live with that so I swapped to a ’87 TBI tank, ’87 TBI sending unit with a Corvette fuel pump to feed the 8.1L the pressure it needs.

GM and AC Delco pn for the switch valve 14029228
http://198.208.187.182/servlet/com.e...rtnbr=14029228

Here is how I had my frame pump mounted. Protected by the cross-member from road debris and also shielded from the exhaust. This contraption is gone now that I have converted to an in-tank pump and a transfer pump to move fuel from the secondary tank to the primary.
http://67-72chevytrucks.com/gallery/...cd8396.jpg?v=0

Re: Tbi swap build thread
 

Thanks for the info and the pics. If i were to use a frame mounted pump witch one would you recomend?

Re: Tbi swap build thread
 

Man, I don’t know. The frame mounted pump I had was a Summit Racing house brand. I hear good things about the Walbro pumps. I actually bought a slightly used low pressure Walbro from a board member, Rust Buster, for my ’72 C20 that I just completed the TBI swap on a few weeks ago. The damn truck is still at my buddy’s getting the exhaust hooked up so I haven’t had a chance to find any bugs with it yet. The Walbro pump is what all the TBI conversion kitters like Howell sell with their complete TBI kits.

Here is the Walbro mounted on my ’72 C20 with a TBI 5.7L. Not a very pretty install but it is not a very pretty truck either.
http://67-72chevytrucks.com/gallery/...cd04e5.jpg?v=0

Re: Tbi swap build thread
 

Mr. Gasket #12D. Summit Racing pn MRG-12D. It is a low pressure/high volume pump. The pump is actually labled as diesel fuel but it will work as a gasoline transfer pump per Mr. Gasket tech line. I am happy with it so far with only testing it in the garage a few times. Moved 1/4 tank of fuel in less than 4 minutes from the secondary to primary tank. Will be making a run to the mountains in a few weeks so I should have real world results soon.
http://67-72chevytrucks.com/gallery/.../mrg-12d_w.jpg

Mounted on a fabricatedcross member between the frame rails. Operated by Painless Wiring electric fuel pump harness kit PRF-50102 (Summit Racing pn) and a toggle switch.
http://67-72chevytrucks.com/gallery/...6fc267.jpg?v=0

Re: Tbi swap build thread
 

Hey Cj

A while back DirtyLarry and I had a bit of discussion going about EFI retrofits and engine swaps. In this thread I posted my setup details - double posting is never a good idea...

http://67-72chevytrucks.com/vboard/s....php?p=2950627


//RF

Re: Tbi swap build thread
 

FYI you don't HAVE to get EFI tanks, just don't run the truck less then 1/4T or so if you are offroad/camber often.

Walbro is a good pump, but in the tank is the best location.

Re: Tbi swap build thread
 

Thanks for the link. That does look like a good way to go. I do have one efi tank with the pump in it. I am going to use that right now and try to go with a stock setup latter.
Thanks, Jamie

Re: Tbi swap build thread
 

From what I have read the vss is used by the computer to see how fast the car or truck is going. The vss is also used to control the egr valve the charcoal canister purge valve, idle speed, and air fuel ratio at speed.

I belive in this way, if chevy did'nt need it why would they spend the money to have it installed in the wiring harness.

How does your truck run with out it?

Re: Tbi swap build thread
 

The truck runs great. The VSS is for the electric speedometers and cruise control, but I'm wondering if it does anything else. If it is supposed to control the issues you mentioned above, but is unable to, would you get a code?

Re: Tbi swap build thread
 

Well being that you have a 4 speed trans what did you do with your prn/nurteal wire for the computer?

Re: Tbi swap build thread
 

Park/Neutral? That's some thing I would have to check into; I don't recall. The truck has the original Muncie 4 spd.

Re: Tbi swap build thread
 

B-10 is the signal wire # for the ecm that is you park nutreral switch wire. If it is grounded the computer thinks it is in nuteral all the time and will not throw a ses light. A-10 is the vss signal wire. it runs the the vss sensor it's self.

Re: Tbi swap build thread
 

So what you're saying is if there is no VSS signal going to the ECM, it will not run as efficiently as it could? And also stay in open loop? Now that you mention it, B-10 must be grounded because I don't get an SES light other than start up.

Re: Tbi swap build thread
 

Are you using a stock, or a aftermarket harness?

Re: Tbi swap build thread
 

Stock harness from an 89 pickup.

Re: Tbi swap build thread
 

Well I would re-trace the wires to see what they are doing.

A-10 is a brown wire from the ecm, and B-10 is a org wire with a blk strip on it. let me know what you find, I am just staring my swap as you can see. :chevy:

Re: Tbi swap build thread
 

P/N line Orange/black wire is grounded by a P/N switch when in park or neutral position. P/N switch ECM input is used by ECM to compensate idle speed when additional engine loads (AC, PS pressure, etc) are present while in drive and within idle speed range. ECM commands IAC to add additional 50 to 75 RPM over commanded idle speed under such conditions. In your case (manual tranny) leave p/n wire open (i.e always in 'drive')

VSS is extremely important for complete EFI operation. It is unfortunate that many omit VSS during conversion. In your case, having 4 speed manual, it is imperative to have a functioning VSS. Since you have 1227747 ECM you'll need to have 2-pulse square pulse VSS inline unit. These are readily available (JTR, others). VSS provides vehicle speed to ECM which uses this input to accurately set fuel mixture and timing. One common problem with absent VSS and manual tranny is a severe drive train jerking during deceleration. This due to inability of ECM, which uses TPS, MAP and VSS inputs, to enter DE/DFCO mode (Deceleration Enleanment / Deceleration Fuel Cut Off).

When the ECM detects a sudden drop in throttle position and engine load, it reduces the injector pulse width while continuing to monitor engine load and vehicle speed. The purpose of DE is to produce a lean fuel mixture by reducing the amount of fuel gong to the engine. DE mode conditions are determined by ECM on a continuous bases provided that 1) Vehicle speed is above XXMPH (this depends on EPROM calibration value), 2) engine load decrease is below a limit value (this parameter also depends on EPROM calibration value), and 3) Filtered %TPS drop is <1%.

The difference between DE and DFCO parameters is that DFCO parameters are based on fixed values stored in EPROM. The DFCO fuel mode is entered after moderate to heavy acceleration then followed by abruptly releasing the accelerator. Usually ECM will transition into DE prior to entering into DFCO mode as the deceleration continues. Interestingly enough operating conditions may or may not cause ECM to command DE exit by itself. However when ECM enters DFCO mode DE is automatically disabled. Usually DFCO is a 'long' term (self resetting) duration event - coasting down hill in gear for example.

Both DE and DFCO are used for emission control, (keeps CATS from being burned up due to excess fuel during deceleration), but the two will effect drive train and exhaust longevity. There are many other ECM controlled parameters that are derived from VSS input.

//RF

Re: Tbi swap build thread
 

Rfmaster,

What you said above about VSS sounds right for 1996 and later OBD II sequential multiport EFI systems but I can’t find anything in any of my older GM STG service manuals for TBI years that state the VSS has anything to do with Deceleration Enleanment or Deceleration Fuel Cut Off. It could be one of the functions that takes place behind the scenes that isn’t really called out in the service manual.

From what I understood, the main sensor to control fuel on OBD I such as TBI is the MAP as it constantly monitors engine load and adjusts fuel pulses accordingly. Once you get into OBD II on sequential multiport things get a lot more complicated and more inline with your description above.

The only function I can find for the VSS in TBI years is to provide a pulse signal to the DRAC for the speedometer, RWAL ABS module, and cruise control module. The VSS isn’t even mentioned anywhere in any of the drivability symptom flowcharts or anything other than inop speedometers, cruise, ABS, etc.

For what it is worth, my 8.1L running multiport EFI on a Delphi MEFI-4 controller (similar to a GMPP RamJet engines and GM Marine engines) doesn’t have any VSS inputs either to run, and run well even with a manual trans. The whole MEFI-4 system is an entirely weird deal anyway.

I know you are an engineer and know this stuff a lot better than any of us but are you sure about the VSS function on TBI?

Re: Tbi swap build thread
 

I thoght that on OBD II they did not use a vss sensor, but the ecm got it's signal from the abs computer.?

Re: Tbi swap build thread
 

Many thanks for taking the time to post your info and progress. This will be a great help to myself and I am sure many others when I get to my drive train. Right now I have an 88 GMC for the donor but may look for the last year of TBI.

Re: Tbi swap build thread
 

VSS is still used today to provide data to the PCM/ECM for engine controls, speedo, cruise, trans shifting scheduling, torque converter lockup, etc but not ABS. These days, there is actually a wheel speed sensor at each wheel to provide input to the ABS module to control 4 wheel ABS system and traction control if equipped. In the TBI days the trucks only had rear wheel ABS which the rear wheel speed input to the ABS module was read from the VSS sensor on the tail shaft of the transmission.

Re: Tbi swap build thread
 

My apologies - 7747 does not have DFCO - MPH threshold, which is used in 8746 ECM found in TBI passenger cars. Also, DE is mapped to MAP and RPM threshold in 8746.

Now that I looked back at my notes I know where I got confused - in my conversion I used 16136965 from 1991 B-Body which just happens to be almost pin compatible with 1227747 (there are couple more control outputs and MAT input) which in its stock form uses speed threshold for DFCO. In the end it did not matter to me at all since I have converted to EBL which provides full control over DE and DFCO.

VSS in 7747 is used primarily for TCC control, Knock retard, Highway SA, EGR, & Idle speed compensation.


//RF

Re: Tbi swap build thread
 

So, rf & Dirty Larry, is there any benefit to installing a VSS in my ride? As mentioned above, it is an 89 setup, so there is no DRAC in this setup. I'm still using the mech speedo and have no cruise. THANKS FOR YOUR HELP!

Re: Tbi swap build thread
 

Skidder,

I would venture to say you are good to go without VSS on a manual transmission. With an automatic, yes, you would need it for the torque converter lockup. Your earlier post mentioned a concern with going into closed loop. Closed loop is achieved by the engine coolant temperature sensor (ECT) and O2 sensor inputs not vehicle speed.

My 8.1L with a manual trans does not have a VSS at all. Even though the 8.1L is multiport EFI, mine is running an OBD I speed density calibration system through a Marine MEFI-4 engine controller with a protocol that is very similar to the old TBI and TPI systems of the late 80’s and early 90’s. As far as fuel delivery, the main difference is my 8.1L fires 8 injectors under a higher fuel pressure in batches where as TBI is firing 2 at a lower fuel pressure. Firing the 8 individual coil packs on the 8.1L is what is unique about the MEFI-4 controllers as they are very versatile in programming what they can control….but that is a whole nuther story.

This is one of the reasons I have chose to go with aftermarket harnesses opposed to reworking a donor vehicle harness. First, a donor vehicle TBI harnesses are getting old (last TBI truck was built 15 years ago!) and the harnesses tend to be very brittle and stiff, end connector break at the touch, etc. Second, a creditable aftermarket harness vendor such as Howell or Street and Performance, etc has already put a lot of research into knowing how to properly wire these things. Most of those companies have gone to the manufactures and purchased the original engineering layout drawings to create stand alone harnesses without all the unnecessary circuitry. For $325 a nice fresh harness is hard to beat vs. pulling your hair out trying to rework an old harness only to still have a 15+ year old harness when you are done.

Re: Tbi swap build thread
 

Larry you have a very good point about the old harness on the fact that it is old and the wires are brittle, (mine has been for the most part very managable though) and me and you talked about me buying a harness from Howell. I am right now off work untill the first of the year and I want to get this swap done before I go back to work. Untill I go back to work I really do not need to spend any more money than I have to. So I had the stock harness and decitted to use it. When I decited to do that I thougt while I was searching the net for info on this swap that the info is out there but you really have to look every where for it. So I decited to start this build thread to maybe help other people out that want to do this swap and use salvage parts in the process to save a buck or two.

I really do appreciate the input that people are putting in this thread ( like you and rf).

Got to go and work on my truck now.;)

Re: Tbi swap build thread
 

Well I did not get to work on it as much as I wanted to to day but did get a little done.

First two is a before and after on one side of the motor. This is where the ESC, TPS, MAP, IAC, EGR , and temp plugs are located. You can also see where the wires enter the cab

The others are the wires that I will have to hook up in the cab. They are

B-10 park/neutral
A-5 SES light
A-8 ALDL
A-9 ALDL

Re: Tbi swap build thread
 

Here are some of the wires that I will have to hook up that do not have factory plugs.

The first one turned out fuzzy but it is the 12 V feed wire (I am going to put it to the big post on the starter with a inline fuse).

The second is C-9 this wire goes to the sm post on the stater.

The Third is the switched 12 volt wire. ( I am going to put it on the smaller wire that pluged into the orginal HEI BAT terminal).

The Foruth is the ground wire for the system.

The Fifth pic is the wire that will power the dist. ( I am going to tie it to the big HEI wire that is on the truck now.

Re: Tbi swap build thread
 

Gents

VSS is important as it is not only used for the lock-up torque converter control. The VSS is also used to control the EGR valve, idle speed, and air/fuel ratio. I have to emphasize that the VSS is used to control the idle speed when the vehicle is moving. Without the VSS, engine may have stalling problems under certain conditions, which in itself is dangerous. You can increase minimum idle speed with the adjusting screw and eliminate stalling, but the engine will still not run optimally without a VSS.
Somewhat erroneously many think that running "closed loop" is best for fuel mileage - it is not. In closed loop NBO sensor is being used to monitor the exhaust O2 content and ECM changes commanded AFR. There are ECM's that allow engine to run very lean (15:1 to 17:1) under certain conditions (called "highway lean mode") to improve fuel mileage during - for example steady cruise conditions (no delta TPS, no delta MAP). Without VSS, ECM will not get the correct signals to run the engine for best fuel mileage. So if you are planning to drive long distances and burn less fuel VSS is a must. For my retrofit I used JTR Part #2PRS which is two-pulse per revolution, square wave unit for all TBI installations, 7/8-18 thread, .104" square drive. BTW, I get 17.5 MPG on extended cruises (that's 6500lbs moving at 65 MPH).

//RF

Re: Tbi swap build thread
 

Photos from my swap

It all started innocently enough in the fall of 06 - another tune-up and idle quality and cold starts are hideous with old Q-jet. After a bit of reading I came across a TBI 4.3 swap into a Jeep...
http://www.bustedjeep.com/projects/junkyardtbi.asp

After reading and a quick trip to a local pull it your self JY


ECM / Harness /Dizzy (useless) / sensors
http://67-72chevytrucks.com/gallery/...re031-crop.jpg

It took over 2 hours at JY to carefully pull this tangled mess without breaking anything in the process. The firewall grommet in this B body used epoxy like filler to keep everything together - nasty to remove.
http://67-72chevytrucks.com/gallery/...Picture033.jpg

After another 2 hours the harness was hanged like a deer for cleaning.

http://67-72chevytrucks.com/gallery/...cture040-r.jpg

Removed wires and vacuum lines used by AC control circuits

http://67-72chevytrucks.com/gallery/...Picture042.jpg

Final harness, arranged and labeled
http://67-72chevytrucks.com/gallery/...to056-crop.jpg

Surprisingly enough wires were in excellent shape - no breaks this was a low millage car. I did had to replaced several connectors - broken tabs and shorter overall runs. However in my next conversion I will get new harness - just to save time! Initial harness fitting:

http://67-72chevytrucks.com/gallery/...to117-crop.jpg