Stock alternator to 12 SI alternator
 

I hope this will make things a little clearer on this swap.

The trucks stock alternator and external regulator have always been a weak spot for these trucks if you add many electrical accessories to them, The stock alternator was a 37amp which was plenty for a plain truck. But who leaves their truck to plain??:lol::lol::lol:

Anyway I hope this clear's up some of the confusion and questions on this swap.

Take the stock alternator off the truck and replace which ever you decide to use. I like the 1985 Buick Riviera, 5.0L (307Y engine), with Heavy Duty options and Air Conditioning.”
This mod doesn't require any new wiring. It just re positions what's already there.

Ok for the choices you have for the install.

Picture #1 is what you start with.
Picture #2 is with the jumpers @ the regulator used.
Picture #3 is stripping the harness cover back and running the brown & red wire straight to the alternator. Much cleaner install.
Both ways work fine and as Vette has stated before, the system works as it's suppose to from the factory.

There is another option that works but it doesn't use the system feature of sensing voltage drop and kicking up the voltage. So I'm not going to address it here.
Side note.
This mod works for 50,60 & 70 model GM cars as well.
If you have any question on this mod please feel free to ask but keep the questions to this mod only.:chevy:

Re: Stock alternator to 12 SI alternator
 

Thing I am having an issue with is I cannot find the thread which shows which light on the dash and wire therefore, is the resistor wire.

VV mentions somewhere in one of these threads about installing a failsafe off the keyed switch just in case the bulb goes out.

Which bulb on the dash is he speaking of? Of course I am inquiring about the 7 gauge panel.

Re: Stock alternator to 12 SI alternator
 

The red light under the gas gauge. The brown wire is the resistor wire. The only thing I know of is for the newer CS style alternator's not this one. :chevy:

Re: Stock alternator to 12 SI alternator
 

There is 2 red lights under the gas gauge to my understanding. Yes, Andy, the brown wire. I worry about that bulb or the printed circuit going out leaving me with a new issue, and costs.

I am redoing a new underdash used harness, as the leaks I used to have left me with a never ending mess.

Re: Stock alternator to 12 SI alternator
 

If I understand this correctly, the red wires that connect to the plug and the small bolt on the back of the alternator also connect to each other?
What is the white wire (18 B/W?) with the fuse and the black wire engine harness with the fuse? Are those stock wires or something I need to add as well? I'm referring this picture.

https://i.imgur.com/3pWQ18c.jpg

Re: Stock alternator to 12 SI alternator
 

Re: Stock alternator to 12 SI alternator
 

Okay, that makes it a little clearer. I cut the brown & red wires at the old regulator and plan to use those to connect to the plug on the alternator. Is that correct? The wires that were on the back of the old alternator were blue & black, if memory serves me correctly.

Re: Stock alternator to 12 SI alternator
 

Yes you are correct and all you need is this connector that you can get at most of the auto parts stores. about 5 buck if I remember.
Just use butt connectors or solder the red to red and brown to brown so that the plug connects the brown wire to no.1 and the red to no. 2.

The two wires were 16 gauge dark blue and 16 gauge white from the regulator.; You wont need those anymore. VV


Attachment 1983470

Re: Stock alternator to 12 SI alternator
 

I already have that connector hooked up. Thanks Andy & VetteVet for the help, I really appreciate it.

Re: Stock alternator to 12 SI alternator
 

Your welcome. Let us know how it turns out.:chevy:

Re: Stock alternator to 12 SI alternator
 

Will do. Right now I'm experiencing a "little" project creep ;) It was originally supposed to be get it mechanically sound and drive it. Just like all my other projects, I got the while I'm here bug. Also, I want to do it once and be done with it. I installed relays for the headlights (GMC) and of course decided that the buckets needed to be replaced, which of course requires new springs and adjusters. Then, while I was there I might as well upgrade to the newer style headlights . . . chick-pona-nona-wana.

I picked up these little boogers from Amazon delivered today, as well new copper connectors. I just wanted to upgrade the alternator! :banghead:

https://i.imgur.com/ePvjLSv.jpg

Re: Stock alternator to 12 SI alternator
 

Okay, If I have this right, to bypass the external Regulator, I connect the blue and yellow wires coming out of my Alternator to the red and brown wires, respectively, in the Regulator plug. This permits the Internally-regulated Alternator to take over for the original external Regulator and my battery should charge?

Re: Stock alternator to 12 SI alternator
 

You should have the red wire at the external regulator jumped to the blue wire that goes back to the alternator. Marked #1
The brown wire @ the external regulator jumped to the white going to the alternator. marked #2

PS, the wire colors really don't matter as long as you jumper them to the right spot. I don't know where you got the yellow wire from???


Per this drawing.:chevy:

Re: Stock alternator to 12 SI alternator
 

Sorry, I stripped back the casing and found what was once white is now yellow. Kind of like old men's teeth, which I know altogether too well!

Re: Stock alternator to 12 SI alternator
 

okay, smoke under the dash. Black wire with white stripe. Have I got something reversed? My Alternator is a bit different from the earlier pictured model. That's a new plug from FLAPS. The blue wire shown connects to the white harness wire and the black connects to the blue harness wire. As per how the previous stock plug was.
https://live.staticflickr.com/65535/...4dbbd61a85.jpg

Re: Stock alternator to 12 SI alternator
 

I'm sorry but I'm not following you with your wire colors. You are gonna have to strip the harness from the old external regulator. Then wire it like the drawings. I don't know what you have and your picture doesn't show me anything. The plastic connector is marked 1&2 and the wires must go to the right spots no matter what color they are. :chevy:

Re: Stock alternator to 12 SI alternator
 

If you have smoke under the dash there is more than meets the eye. Read my thread wanting help please in this forum.

I have had both heater switch issues and ignition switch issues for the last couple years. Just this last time out the big brown wire(heater) and large purple wire had melted through each other and I was driving down the road when the starter engaged.

Ignition switch cooked next far as I can tell.

Re: Stock alternator to 12 SI alternator
 

Re: Stock alternator to 12 SI alternator
 

Smoke under the dash means something burned. It would be wise to strip the harness of the black tape and look for burned wires. That discoloring you see in the thread posted by Andy means overheating, overamperage of the wiring system.

Sometimes you can get away with it. Other times it leads to problems down the road as in my system. I have had to replace the Heater Harness, Heater Switch, Ignition Switch over 3 times in the last couple years.

I am sick of it, my electrical buddy informs me if you feed the system more power an electrical motor will demand that from the system. As in Heater on High, unregulated load. Another words, you will pull more amps through the system than the wiring will handle. Especially if you put in a higher amp alternator. If you put in a bigger guage wire in combo with the higher amp alternator this compounds the matter. Stock gauge wiring acts as a restrictor (i.e. smaller water pipe) to only allow a certain amperage to flow through it.

This specifically applies in my situation due to having a externally regulated alternator. The regulator allows it to push out more amps than an internally regulated unit IF I am correct.

I carry a fire extinguisher in my cab just in case.

Re: Stock alternator to 12 SI alternator
 

Re: Stock alternator to 12 SI alternator
 

I would start tracing all the main feeds. Both under the hood and under the dash. They are all 12 gauge, Red and pink for feeds, heater is run by a brown one, and the solenoid is purple.

Under dash harness is easier to trace by removing in one unit. You will most likely find that easier to remove by also removing the dash gauge cluster. From there tracing all the wires will be much easier.

Checking continuity and resistance is a good idea at this point. Most of the old contact points on the crimp connectors.

It is tedious, most guys get too frustrated and just buy a 4-6 hundred dollar replacement. I found 3 old harnesses for 80 bucks and used the good parts, wires from them.

Almost got mine running today, have to check my flywheel for out of round then shim the starter appropriately adding a starter brace.

Oh, and yea, my nerves are pretty cooked right now.

Re: Stock alternator to 12 SI alternator
 

I have been considering a new wiring harness for under the dash. However, must confess being lazy and cowardly about the whole thing. It's a project I've done in the Studebakers a number of times for much the same issue. Having the modular approach Chevy takes on wiring makes the job easier. However a Studebaker harness is half the price.

However I must straighten out this issue with my Alternator first. Can't do that till it stops raining, hailing, and snowing by turns.

Re: Stock alternator to 12 SI alternator
 

Thanks for the help! All better now, I hope!

Re: Stock alternator to 12 SI alternator
 

Regarding post #19... "The regulator allows it to push out more amps than an internally regulated unit IF I am correct."

No, not correct. The load draws current depending on it's current needs at X voltage (current increases with voltage). The source doesn't push current. A new style alternator may regulate the voltage at a higher value, allowing more current at X load though. With wiring in decent shape the difference shouldn't be an issue.

One issue is bad wiring/connections that act as heaters, which can cause problems but this is true regardless of the alternatore/regulator combination.

Re: Stock alternator to 12 SI alternator
 

Thanks for clarification, and it is also what I suspect, that would be correct from electrical theory. My personal issue is different than the OP. My wiring (original) is cleaned up nice!

I read somewhere that the internally regulated alt units have better control of the voltages. If you looked at the next gen of trucks with HEI they have internally regulated units.

Crankshaft coalition wiki site says HEI modules do not like high voltage spikes.

Re: Stock alternator to 12 SI alternator
 

Few months old thread, but exactly what I'm going to do shortly. Should the 12R wire be upgraded to a bigger gauge. I assume 12R stands for 12 gauge, Red. Is there anything special about the wiring to make the amp meter work? Per info I found it looks like 12 gauge will flow 41 amps. Enough for a stock 37 amp alternator.

Re: Stock alternator to 12 SI alternator
 

Here'e a page that explains how to wire the amp gauge (and volt gauge).

http://6066gmcguy.com/ammeter.html

As for the 12 gauge wire, I think that should be fine, but I'm no expert. I used 10 gauge, I wanted to err on the side of caution in case I add electric fans.

Re: Stock alternator to 12 SI alternator
 

It depends on what you mean by "the amp gauge". That site does not show how to wire the stock amp gauge from a 67-72 Chevy/GMC truck. It covers how to wire an amp gauge that has a built-in shunt, so that would be an aftermarket or some other model year or make amp gauge. The stock amp gauge for 67-72 uses an external shunt. The shunt is the 12 gauge red wire that runs between the battery and alternator, and in order for that to show all charging and discharging of the battery, no accessories are connected at the battery or starter.

Re: Stock alternator to 12 SI alternator
 

Oops, thanks for clarifying that. I found that site a while ago and bookmarked it for when I wanted to tackle getting my gauges straightened out.

Re: Stock alternator to 12 SI alternator
 

I'm looking at a 100 amp alternator. If I read the charts I've found correctly, I should probably have a 6-8 gauge wire off of the alternator

Re: Stock alternator to 12 SI alternator
 

The question is, where does that wire run to? If you have a load that will be drawing a bunch of current, you can run it to that load. If you expect the battery to supply a bunch of current to a device when the alternator is not running, then I suppose the wire from the battery to the alternator and that device also needs to be fat.

I don't have any big loads to worry about although I have a big modern alternator, so I didn't do anything to the stock wiring. I suppose it will be a good idea for me to add a fusible link at the alternator to reduce the risk of the alternator cooking my 12 gauge wiring if I have a short.

If I were to add something that hogs a lot of electric current, I think I would power it from the alternator with a fat wire and use a relay to only connect that device when the alternator was running. The CS144 alternator I have supposedly has a tach output that I would send to a driver/computer for a relay. I can't think of any big current draw that I want to add. Electric fan doesn't make much sense since the engine is right there and works with a mechanical fan far better than converting rotational power from the engine to electricity and then converting that electricity back into rotating a fan. That would be very inefficient to do that energy conversion twice. Electric fans are for front wheel drive cars when the engine sits in the engine compartment sideways. Just my rambling opinion.

Re: Stock alternator to 12 SI alternator
 

This seems like as good a thread as any to post this question...
I'm sorry I can be so long-winded. The more details the better.

I've eliminated a voltage regulator before on a '69 Camaro. I did it when I did an LS swap and used the 2006 engines alternator. I did it like picture #2 in the original post with an adaptor jumper plug. Worked fine. I didn't have a roundy-round ammeter or volt meter because I had a Dakota Digital cluster...and didn't change anything in the dash wiring.

The previous owner of my truck swapped in the current '79 Nova 305.
These pics show how he wired my alternator, which has zero numbers or marking on it at all. Reman cheapy of unknown type.
It works fine. They put a Voltage gauge in which functions fine.

Now, the voltage regulator is STILL connected.
The original AC Gen. wiring is coiled up and Zip-tied intact and out of the way. The truck was obviously a 6cyl. with points and coil from the factory.

They have a 10ga wire straight from the battery+ to the BATT lug on the alternator. You can see that it's jumpered over to what I believe is pin #2 with a smaller gauge red wire.
Pin #1 has a random white 12ga wire connected with a large diode to prevent backfeed. I haven't looked at the diodes specs yet. I'm assuming the cheapy alternator he put in doesn't have that circuit so he spliced that diode inline.
That wire is run around to the HEI where it's spliced into the ignition wire. That wire is plugged into one of the Unfused spades in the fuse panel.

That seems OK for making the circuits and alternator work for a 1-wire system...but it's done in a weird way.

I'm gonna guess that alternator is at least a +/-60 Amp unit.
My question is how is all this working with the voltage regulator still hooked up? And what trouble am I looking at leaving it this way? Previous owner drove it like this for 2 years. To top it off, there's 2 Viair compressors powered by a solenoid in back for the air bags. It's powered straight from the battery.

Since all my original wiring is still in place, I guess I should rewire the charging system, but if it's working I'm wondering if I should leave it.
Oh, and I ALWAYS have a fire extinguisher in my cars.

Re: Stock alternator to 12 SI alternator
 

One thing you're missing from your current arrangement is a functional dash warning light for your alternator. For that to work, you would need to connect the brown wire from your original harness to the alternator, as described at the beginning of this thread.

My suggestion would be to eliminate your external regulator and its original 4-pin connector, and extend the wires from the original harness over to your passenger-side-mounted alternator. Also, a factory-style alternator connector is available at your local auto parts store. The terminals from your original alternator connector can be popped into this connector housing as well, if you want to reuse your original blue and white wires.

https://www.oreillyauto.com/detail/c...tor/cti0/85841

Re: Stock alternator to 12 SI alternator
 

Thanks
What I didn't include was that the GENERATOR idiot light functions fine also. Other than the fact that it stays on real dim while it's running, it comes on bright when it's supposed to...with the key to Ignition.

The other thing I noticed is a 15A fuse taped into a spliced wire on the back of the Volts gauge, which is spliced into the 12Ga pink Ignition switch wire. That's another new one on me...never heard of that before.

I've got connectors and everything I need...just trying to make heads or tails of HOW this damn thing works and isn't on fire. 😁

Re: Stock alternator to 12 SI alternator
 

Some people are interested in getting something wired up not necessary correctly, but getting it to the point where it mostly works and doesn't seem to catch on fire, and they are satisfied. It's a matter of attention to detail. With the original alternator wires zip tied and out of the way, the regulator is mostly disconnected and not doing much. It may be contributing to the generator warning light somewhat working.

The #2 terminal is OK to connect directly to the batt terminal of the alternator, it is how the alternator senses how much voltage is on the battery wire so it knows how much to output. That wire would normally be connected to the battery wire at some distance from the alternator, such as the point at which the wire connects into the main harness by the driver side headlight. If it is connected remotely, it gives the alternator a better idea of what is going on with the voltage in the harness so it can better regulate output. The #1 terminal is connected to a resistor wire in the cab or to a diode, and provides a way to turn the alternator on or off. It is called the exciter wire. If you have a warning light instrument cluster, this wire also (normally) runs the generator warning light.

Here's a thread that describes the setup with the diode, and also shows the wiring with the generator warning light, and talks about where on the harness the sense wire is best connected. http://67-72chevytrucks.com/vboard/s...d.php?t=604881

Re: Stock alternator to 12 SI alternator
 

Thank you...

Re: Stock alternator to 12 SI alternator
 

Thanks for this write up. I will be doing option 3. To be clear the alternator shown in your pic is for a 1985 riviera. I’d like to just do as you did. Also will it mount in stock location with stock brackets . I have a 1972 k10 running the alternator on the drivers side. 350 engine. Again thanks ja much

Re: Stock alternator to 12 SI alternator
 

Please check out the threads in my FAQs at the top of the electrical forum
http://www.67-72chevytrucks.com/vboa...d.php?t=815300