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Old 01-31-2020, 04:52 PM   #1
Andy4639
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Thumbs up 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??

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.
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Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 02-03-2020, 12:13 AM   #2
toolboxchev
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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.
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Old 02-03-2020, 10:29 AM   #3
Andy4639
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Question Re: Stock alternator to 12 SI alternator

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Originally Posted by toolboxchev View Post
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.

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.
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Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 02-03-2020, 11:23 AM   #4
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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.
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Old 02-15-2020, 07:56 PM   #5
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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.

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Old 02-16-2020, 06:09 PM   #6
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Re: Stock alternator to 12 SI alternator

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Originally Posted by maverickmk View Post
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.

The 2 black wires with the 2 small 4 amp fuses are stock original for the amp-meter to work. They stay as they are.
The red wires do connect to each other in the wiring harness. But don't jumper them at the alternator plug.
This want give you the correct reading.

The picture shows the stock bulk connector that is up by the drivers side head light. The bigger red wire goes to the bolt on the back of the alternator. The smaller red wire that was connected to the external regulator now goes to the #2 terminal.
The brown wire that was connected to the external Regulator now goes straight to the #1 on the alternator.
The white wire is terminated and not used.
You should run the small black ground wire over to the alternator also.
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1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver
Seeing the USA in a 71


Upstate SC GM Truck Club
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Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 03-12-2020, 09:43 PM   #7
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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?
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Old 03-12-2020, 10:27 PM   #8
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Thumbs up Re: Stock alternator to 12 SI alternator

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Originally Posted by studeclunker View Post
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?

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.
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Seeing the USA in a 71


Upstate SC GM Truck Club
2013,14 and 2016 Hot Rod Pour Tour


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Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 03-13-2020, 12:58 AM   #9
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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!
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Old 03-13-2020, 05:22 PM   #10
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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.
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Old 03-13-2020, 10:23 PM   #11
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Thumbs up Re: Stock alternator to 12 SI alternator

Quote:
Originally Posted by studeclunker View Post
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.
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.
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1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver
Seeing the USA in a 71


Upstate SC GM Truck Club
2013,14 and 2016 Hot Rod Pour Tour


http://upstategmtrucks.com/



Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 03-14-2020, 04:15 AM   #12
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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.
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Old 03-14-2020, 01:18 PM   #13
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Re: Stock alternator to 12 SI alternator

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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.
I looked that one over before posting here. I don't understand the relevance? Must be missing something?
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Old 03-14-2020, 02:08 PM   #14
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Re: Stock alternator to 12 SI alternator

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Originally Posted by studeclunker View Post
I looked that one over before posting here. I don't understand the relevance? Must be missing something?
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.

Last edited by toolboxchev; 03-14-2020 at 02:15 PM.
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Old 03-14-2020, 03:18 PM   #15
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Re: Stock alternator to 12 SI alternator

The Studebaker Driver's Club has pushed carrying an extinguisher for years. I have one in each of mine. However I haven't yet equipped this truck with one and really should.

This isn't the first burned wire in this system, I've replaced quite a few. Ground wires also. I was wondering where the latest burned wire went as it helps knowing which circuit is overloading.

However, I need to get this truck going as everything else has no brakes and I needed to move a trailer up the mountain. Looks like no trailer up the mountain (due to this current issue) as we are looking at two weeks of snow up there.

Can we spell f-r-u-s-t-r-a-t-e-d?
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Old 03-15-2020, 02:31 AM   #16
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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.
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Old 03-15-2020, 03:12 PM   #17
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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.

Last edited by studeclunker; 03-15-2020 at 03:22 PM.
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Old 03-20-2020, 04:27 PM   #18
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Re: Stock alternator to 12 SI alternator

Thanks for the help! All better now, I hope!
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Old 03-20-2020, 05:50 PM   #19
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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.
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Old 03-21-2020, 11:57 AM   #20
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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.
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Old 08-13-2020, 11:01 PM   #21
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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.
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Old 08-14-2020, 08:49 AM   #22
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Re: Stock alternator to 12 SI alternator

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Originally Posted by tdangle View Post
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.
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.
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Old 08-14-2020, 07:38 PM   #23
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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.
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Old 08-14-2020, 08:48 PM   #24
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Re: Stock alternator to 12 SI alternator

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Originally Posted by dmjlambert View Post
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.
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.
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Old 08-14-2020, 11:25 PM   #25
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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
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