'86-'13 swap questions

[rodstored-72]

I wasn’t sure where to put this I’ll drop it here. I have a ’86 chevy swb and I have installed a ’13 4.8/4L60E combo. I am trying to figure out the physical wire connections and where to make the connections? My engine is a “drop out” so I have the complete uncut engine harness including a reflashed ECM (lt1swap) and the factory “x2” connector. I have also purchased a factory underhood fuse box as well as the factory power cable that runs from the box to the battery. My ’86 harness is factory and I believe to be original to truck. I have the ’13 engine wiring diagrams and have identified all the wires in the harness and wires to the “X2” connector. I have a pretty good idea (I think) of what wires are what and where they go. I just don’t understand where (between ECM and x2 connector??) to make the connections and how to make the connections (physical). I have read builds on here and other sites as well as on lt1swap. Everything is identified I am just not sure how to and where to connect.
Any assistance would be greatly appreciated, my build is in the squarebody builds section as well.
Thank you in advance

[87chevy.com]

not many people use the factory fuse box, so that right there is going to limit 98% of the people here who have done these swaps.
so.. its just like any other swap. identify one wire at a time, ohm test it with a multi meter to verify if its your 1st time, rinse and repeat so you 1, know and 2 make minimal mistakes if any.

make a new fuse box with whatever you can afford. cheap ebay 30$ fuse box that some have used, or research other fuse boxes thats higher quality and uses quality seals and terminals.

ls swap needs minimum
battery constant power to the fuse box
ignition power
starter
fuel pump relay
everything else is strait up wiring diagram.

clint

[rodstored-72]

87chevy.com,
Thank you for the reply. I understand that the factory wiring is not the normal practice. I did not know that when I started this. I was hoping (thinking) that the principles of the aftermarket connections would still apply to the factory wiring. I am trying to keep from having to lose out on the factory harness & spending the $600-800 for a aftermarket harness. I am aware that most of the wires are not going to be used. I think it would be a neat feature to try to use as much of the wire features as possible to utilize them… I dunno know??? !! I guess I am weird…

ls swap needs minimum
battery constant power to the fuse box (using the factory batt. Cable to the factory fuse box from ’13 engine, this should supply the power as required??)
ignition power (I believe the pink or red wires from the ’86, don’t know how to connect to the ’13 wires – at the fuse box or before the fuses??)
starter (the purple wire from the ’86 to the wire on the ’13 but again where to connect before/after ‘13 fuse??)
fuel pump relay (pink wire to the ’13 wire – same as above??)
everything else is strait up wiring diagram. (I follow this… but not know the how/where to the ’13 wires in the harness)

I appreciate your reply…..

[prodjay10]

Send pics.

You need a constant power, you need a key power, ground, and you need power from the start switch, right?

If you have a dummy light to check for power you can see where you can connect. Or just search for a diagram of the fuse box under the dash.

[MDPotter]

I don't know what kind of underhood fuse box you have, but in this situation, the general approach is to power the LS as a standalone system. Integrating it into an original harness is asking for trouble as the wiring is old and may very well have been hacked on through the years. If you haven't already, I would suggest buying a fuse/relay block like this (water resistant): https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Then, using the info from LT1Swap, build this fuse block. You should never have any connection to the battery without a fuse.

My knowledge of working with an original harness in a square body is limited, so I will offer you what I can on a few connections. Looking at the pinouts on LT1Swap.com, the wires that you need to identify and connect externally are highlighted in blue. These wires will not be removed from the X connectors, but they should be loose somewhere as they should be cut from the donor vehicle fuse box. The wires highlighted in yellow can be removed from the X connectors and removed from the harness entirely. Some notes on the blue highlighted wires:

-Brake switch signal-runs to your brake switch under the dash. Gen IV's need 12v signal when brakes are applied. Make this easier by buying this switch if you don't already have this 4-prong style switch: https://www.psiconversion.com/produc.../KIT-1002.html
-High speed and low speed cooling fan relay controls-run to your cooling fan relays (ground signal). Below is a a GM cooling fan wiring diagram that matches how your Gen IV functioned in stock form.
-Starter solenoid (purple)-I believe this can be independent of the LS harness, in that it just needs to get from the starter solenoid to the key switch.
-Fuel pump-your LS harness should have a single wire that provides a 12v signal when the PCM says it's time to run the fuel pump. This wire will run to the fuel pump relay and power will be distributed from there. The rest of the wiring for the fuel pump should be independent of the LS harness and new. I would do 10 gauge due to the demand of the fuel pump and also the length.
-Wires that require ignition or battery hot, run those through fuses.
-MIL control-this wire provides a ground signal when the PCM decides that there is an issue. This is your check engine light.

I know this is a lot of info. I would recommend reading all the info on LT1Swap and browsing through this LSX Swap forum. Any other questions, let us know.

Dual Fan GM Schematic.pdf

[rodstored-72]

Originally Posted by prodjay10

Send pics.

You need a constant power, you need a key power, ground, and you need power from the start switch, right?

If you have a dummy light to check for power you can see where you can connect. Or just search for a diagram of the fuse box under the dash.

prodjay,
Thanks for the reply. I have a build thread on here in the squarebody section. if you are familiar with wiring (LS swaps) if you feel comfortable PM me with contact info & maybe we can discuss further- (possibly pay for help). I have wiring diagrams for the '13 and for the '86, I just don't know how to physically connect to the existing wires.

[rodstored-72]

MDPotter,
thank you for your response, I know I have bothered you so I appreciate your reply. I guess what I am asking is how to connect the '86 wires to the ’13 underhood fuse box. I have the factory ’13 underhood fuse box that makes the connection to the factory “x2” connector which includes all the wires related to the running and sensors of the engine. My original thought was/is that I could “splice” or “connect” the ’86 wires from the firewall connection to the ’13 underhood fuse box. Originally I was/am thinking that I would use a factory connector (IE: “X5” connector) & then splice the corresponding wires to the ’86 wires. I am just not sure where the relays/fuses in the ’13 box all run out from the X2 connector? I am thinking that it is kinda like a “PCB” situation. I guess like the fuses “on top” of the X2 connector are not all the ones for that connector…lol. one question is that I feel like the underhood box would be the same as the fuse/relay block link that you provided in your post. All the fuses & relays for the engine are included. I have the strtr , fans, fuel pump and ETC relays and fuses in the ’13 box, just don’t know how to connect the corresponding ’86 wires to those? I hope this is making sense, I OBVIOUSLY!! Don’t know much auto. Elec. Stuff, but am trying to learn now. I have looked on lt1swap and a few builds on ls1 tech (builders on here too) so from them I have pretty good idea where things go, just not how to connect then to each other. Looking back now I guess I would have (might have to ) go with a psi or (?) harness and fuse/relay box. When I began this I thought that having all the factory wiring was a good thing & that it would be easier & cheaper in the long run instead of trying to piece meal things together… maybe not…

[rodstored-72]

md potter,
by the way I really like your build & your dad's build too... you guys are pretty sharp!!

[MDPotter]

Not a bother at all. I will try to help where I can. I can't say I've examined a factory underhood fuse block to know where the wires go, but I know it's pretty bulky and will have a lot of empty space after performing a swap. Obviously you can buy a complete new harness from PSI that will be plug and play and have the condensed fuse block/relay setup and make connections easy, it's just more money. If you don't mind spending $600, that's probably the way to go. But if you want to save that money and learn about wiring and have the time, you can make your own fuse block and rework the harness yourself. Just be prepared to spend a lot of time on it and don't get in a rush.

But to answer your question, it should be as simple as soldering the wires together and using shrink tube. I did A LOT of that on my harness and no issues.

And thanks for the compliments on the builds.

[Wgesnerjr]

Originally Posted by MDPotter

Not a bother at all. I will try to help where I can. I can't say I've examined a factory underhood fuse block to know where the wires go, but I know it's pretty bulky and will have a lot of empty space after performing a swap. Obviously you can buy a complete new harness from PSI that will be plug and play and have the condensed fuse block/relay setup and make connections easy, it's just more money. If you don't mind spending $600, that's probably the way to go. But if you want to save that money and learn about wiring and have the time, you can make your own fuse block and rework the harness yourself. Just be prepared to spend a lot of time on it and don't get in a rush.

But to answer your question, it should be as simple as soldering the wires together and using shrink tube. I did A LOT of that on my harness and no issues.

And thanks for the compliments on the builds.

I used the factory Underhood box and although it a great learning experience and much cheaper, I would not do it again. As said before, it's bulky and not much is used on it. I thought about using it for headlights, fog lights, a/c compressor, horn, etc. But wound up only running fuel pump, ecm, and starter through it. Not alot of wiring break down on it and a lot of hunting for which wires go to which fuse.

To save time AND money, go with recommendations on LT1swap site for using the original harness and stand alone fuse/relays. I would do it that way if I could go back.

[rodstored-72]

Originally Posted by Wgesnerjr

I used the factory Underhood box and although it a great learning experience and much cheaper, I would not do it again. As said before, it's bulky and not much is used on it. I thought about using it for headlights, fog lights, a/c compressor, horn, etc. But wound up only running fuel pump, ecm, and starter through it. Not alot of wiring break down on it and a lot of hunting for which wires go to which fuse.

To save time AND money, go with recommendations on LT1swap site for using the original harness and stand alone fuse/relays. I would do it that way if I could go back.

Wgesner,
Thank you for the reply. I agree that maybe knowing now... I might have (still might?) just used a psi harness but...… would you share on how you "attached" the wires to the underhood fuse box? as indicated I have the diagrams for the box, connector and all the pin numbers. I don't know how to connect the truck wires to the fuse box? do the wires get connected directly to the fuse/relay "tabs" from the bottom of the fuse box? example would be connect the starter truck wire to the underhood fuse box starter relay or fuse? and doing this by "connecting" the wire directly to the corresponding fuse/relay tabs from under the fuse box? or do I "splice" the wire to the corresponding wire before the connector into the fuse box?

thank you again for time & response....

[57taskforce]

I used the wiring diagrams on lt1swap to put the harness for the 6.0 together for my truck. I used the parts he describes on that site for the fuse holders and relays. All I have to do is hook up ground, key hot, and constant hot and also the 12v supply wire to the fuel pump. I looked into using the factory fuse box and this ended up seeming a lot easier to me and I was able to weed out all the circuits I didn’t need or care to run for my application. It came out looking like this.

[rodstored-72]

57 taskforce,
Thanks for the reply. since this is a daily driver situation I am needing to keep all the emissions stuff intact so my impression is in trying to keep as much of the factory wire components in tact. I agree that the main wires to connect are minimal, I am just not sure where the truck wires are to connect to the harness wires and how. I am still leaning to trying to use the factory fuse box as the harness connects to it and is clean connection.
thanks

[MDPotter]

Are you subject to emissions testing? When we talk about removing emissions stuff, we're talking about components that are not required for the engine to run, but to pass emissions tests.

Pictures would help us understand your questions too.

[Wgesnerjr]

Having the wiring breakdown the underhood box will help. I did a lot of hunting and pecking to find which fuse went to which relay, etc.

The yard that took my engine out gave me a lot of "pigtails" on the bottom of the box. They did not cut the plug that went to the engine or PCM, but everything else was cut about 2 inches from the plugs underneath. I spliced each of the truck wires to the pigtails to make the fused and relays work.

So if you're looking for exact connections, I didn't document. sorry. I know this will one day come around and bite me in the @$$.

However, in another thread I saw this aftermarket box. I think this would have been a better option than the underhood block.
https://www.michiganmotorsports.com/...0aAmpDEALw_wcB

[rodstored-72]

Originally Posted by MDPotter

Are you subject to emissions testing? When we talk about removing emissions stuff, we're talking about components that are not required for the engine to run, but to pass emissions tests.

Pictures would help us understand your questions too.

potter,
yes Arizona requires emissions per the year of the vehicle. I believe there is provisions related to swaps... still need to investigate with AZDMV. I believe that the emissions will need to work per year of the truck. I would like to keep the engine emissions intact just for ease of future. I will add pictures into my build thread & reiterate things here.

[57taskforce]

Originally Posted by rodstored-72

57 taskforce,
Thanks for the reply. since this is a daily driver situation I am needing to keep all the emissions stuff intact so my impression is in trying to keep as much of the factory wire components in tact. I agree that the main wires to connect are minimal, I am just not sure where the truck wires are to connect to the harness wires and how. I am still leaning to trying to use the factory fuse box as the harness connects to it and is clean connection.
thanks

I’m not sure honestly where your going with that? It’s all up to you which circuits you keep or delete.... there’s really anything much in that huge wiring mess that corresponds to emissions. As far as I can think (correct me if I’m wrong) the only emissions systems on most of the ls stuff is pcv, evap and cats... I know some of the early ones had egr but that’s a small number I believe. You can easily control evap and the rear 02 sensors thru the ecm as that’s how they are controlled to begin with. You don’t need the whole fuse box for that. But if you’d like the whole box that’s fine too just not necessary for emissions.
Edit. The computer has the outputs in the connectors for all the emissions related components. All you have to do is leave those circuits pinned in the connectors and hook them up to the individual components they control like the rear 02’s or the purge valve, etc. The advantage for me in not using the factory fuse box is it’s much simpler to wire everything in and trouble shoot if there’s issues not to mention it takes up way less space. For my setup there’s 4 relays and 4 fuses and that’s it. You can add more relays or fuses easily if need be. Again if your set on the factory box no worries I totally respect that.

[rodstored-72]

Originally Posted by Wgesnerjr

Having the wiring breakdown the underhood box will help. I did a lot of hunting and pecking to find which fuse went to which relay, etc.

The yard that took my engine out gave me a lot of "pigtails" on the bottom of the box. They did not cut the plug that went to the engine or PCM, but everything else was cut about 2 inches from the plugs underneath. I spliced each of the truck wires to the pigtails to make the fused and relays work.

So if you're looking for exact connections, I didn't document. sorry. I know this will one day come around and bite me in the @$$.

However, in another thread I saw this aftermarket box. I think this would have been a better option than the underhood block.
https://www.michiganmotorsports.com/...0aAmpDEALw_wcB

I believe this is what I am trying to do I am just not sure how to? I guess I am going to try to find the other bottom connector(s)… I was thinking along these lines so I believe that the only connector I need to find (get) is the "X3 and or X5" connector. any "recollection" you might have or willing to offer would be very greatly appreciated.

[rodstored-72]

57 taskforce, I may have miss lead in my post.. I am not just worried about the emissions, But my main goal or original thought process was to not have to "rebuild" the harness or throw it away. I was thinking that since it is intact and worked, then I could try to do as wegner did (stated above). My wrong thought process was not knowing that trying to do this was not as common as I thought it would be. looking back it seems to be easier to just do aftermarket harness, but for now.. I still feel I am ahead, it is just taking longer then I was wanting or hoping... thank you for your input and thoughts they are appreciated and noted...

[rodstored-72]

ok.. so I posted this in my build thread in the 73-87 section but I will post here too.. just to get you guys to do some thinking...

"stump the chump" time... anybody know what this connector is? it has 18 wires and was clipped below the factory fuse box & connected to something under the fuse box. I don't believe that it went to the fusebox though..
thanks!!

[aknovaman]

Go here and download the manual for your year of chassis/engine. Its a huge pdf but has all the schematics and connector pictures. The answers to all your wiring questions are 'hidden' in there.

https://www.gmupfitter.com/pages/body-builder-manuals

[rodstored-72]

aknovaman,
thank you for the link. I do already have the electrical info listed on that site. I am going to try to get the other connector pigtails for the underhood fuse box.

thanks!!

[bigmoe]

I was able to find someone to rework my 08 harness, remove the unnecessary wires and put a small fuse/relay box on the end. It was cheaper than buying a whole wiring harness and way easier to install.

[aknovaman]

FYI

Attached is a zipped a spreadsheet for the E38 EFI harnesses. It shows all the wires to retain for standalone config.
Let me know if you have other questions.
Enjoy.

[rodstored-72]

aknovaman,
thanks!! I have downloaded and will look at it. I have picked up the other harnesses for the fuse box. I have separated them and getting ready to label the wires per the diagrams. hopefully I am starting to see the light at the end of the tunnel..... hope!!!