1963 c20 alternator/wiring harness adaption

[Millie63C20]

It’s my first time ever doing electrical and I need some help adapting a wiring harness that only supports internally regulated alternators to an externally regulated alternator. Here are the original and new wiring diagrams.

 

The goal is to have the generator light on the dash also work.

 

Thank you for your help

[Bloo]

Your diagrams did not post for some reason.

 

It is different, and there are more wires. Sounds like you will be making your own little alternator harness. By c20, do you mean Chevrolet pickup? If so, I have a 66 c10 Suburban with an externally regulated alternator setup and an idiot light. I may be able to answer some questions.

[TerryB]

Bloo, tap on the word “here” in the post and they will show up.

[Millie63C20]

1 hour ago, Bloo said:

Your diagrams did not post for some reason.

 

It is different, and there are more wires. Sounds like you will be making your own little alternator harness. By c20, do you mean Chevrolet pickup? If so, I have a 66 c10 Suburban with an externally regulated alternator setup and an idiot light. I may be able to answer some questions.

https://drive.google.com/drive/folders/1-9zBvEUmtMimYcwOAIUxl2HmAZHvpwSt
 

yea it’s a pickup. Im sure anything you could  tell me would help.

 

thanks 
 

 

[Bloo]

Oooooops.. I didn't see the link.

 

Lets start with the charging circuit (big wire). On the original setup, there was a pigtail on the battery cable. It ran to the horn relay. Another piece of wire ran from the horn relay to the big post on the back of the alternator, completing the circuit. A chunk of metal on the side of the horn relay functioned as a shunt for an ammeter on the trucks that had it. Most didn't, but Chevy wired them all that way.

 

The aftermarket harness looks like it has the charging circuit running down to the other end of the battery cable at the starter, with apparently a fuse? This is more or less what GM did later on, except they would have used a fuse link. The less connections and the less wire length you have in this circuit the better. I think you can probably do it this way instead of running it through the horn relay if you want.

 

The jumper the new harness has from the alternator's big terminal over to a little terminal will not be used.

 

The brown wire coming out from the firewall connector should be the idiot light. You should probably verify that it really is. The underdash harness in these trucks are different on ones with an ammeter instead of an idiot light. If it has ever been changed without changing the underdash harness, things can get really confusing, at least on a 66, and its probably the same on yours.

 

Here is what you should see under the dash: The socket for the idiot light (GEN) should be the floating type with 2 wires (no ground). One wire should be switched power that is live with the ignition on. The other one should be running out through the firewall and end in that brown wire that the harness maker intended you to hook to an internally regulated alternator. If that is all true, Grounding the brown wire with the key on should turn the GEN light on.

 

The brown wire just described now needs to connect to the voltage regulator, terminal 4.

 

You will need to make a little harness to hook everything else up. It will be 4 wires that run from the alternator to the regulator.

 

it would be 3 wires if you were running the charging circuit through the horn relay like Chevy did, but I am assuming for the moment you are doing the charging circuit (big wire) the modern way.

 

The four wires are as follows:

 

1) Ground. Bolt it to the alternator case (there's an empty screw hole on the back somewhere intended for this). Put a big ring terminal on the other end and attach it to one of the bolts holding the regulator to the truck.

 

2) Field. This is the regulator's control wire. It is blue on my truck. It connects to the F terminal on the regulator. On my alternator it connects to the spade furthest from the large post. It is probably marked F at the alternator end too, not sure about that.

 

3) Stator. This is hot when the alternator is turning. It is a white wire on my truck. It runs from terminal 2 on the regulator (right next to "F) to the other spade on the alternator.

 

4) 12v Hot. This would normally come from the horn relay. It is just battery hot. Drop another ring terminal over the big hot post on the back of the alternator. Connect it to terminal 3 at the regulator end.

 

Edited February 18, 2021 by Bloo (see edit history)

[Millie63C20]

13 hours ago, Bloo said:

Oooooops.. I didn't see the link.

 

Lets start with the charging circuit (big wire). On the original setup, there was a pigtail on the battery cable. It ran to the horn relay. Another piece of wire ran from the horn relay to the big post on the back of the alternator, completing the circuit. A chunk of metal on the side of the horn relay functioned as a shunt for an ammeter on the trucks that had it. Most didn't, but Chevy wired them all that way.

 

The aftermarket harness looks like it has the charging circuit running down to the other end of the battery cable at the starter, with apparently a fuse? This is more or less what GM did later on, except they would have used a fuse link. The less connections and the less wire length you have in this circuit the better. I think you can probably do it this way instead of running it through the horn relay if you want.

 

The jumper the new harness has from the alternator's big terminal over to a little terminal will not be used.

 

The brown wire coming out from the firewall connector should be the idiot light. You should probably verify that it really is. The underdash harness in these trucks are different on ones with an ammeter instead of an idiot light. If it has ever been changed without changing the underdash harness, things can get really confusing, at least on a 66, and its probably the same on yours.

 

Here is what you should see under the dash: The socket for the idiot light (GEN) should be the floating type with 2 wires (no ground). One wire should be switched power that is live with the ignition on. The other one should be running out through the firewall and end in that brown wire that the harness maker intended you to hook to an internally regulated alternator. If that is all true, Grounding the brown wire with the key on should turn the GEN light on.

 

The brown wire just described now needs to connect to the voltage regulator, terminal 4.

 

You will need to make a little harness to hook everything else up. It will be 4 wires that run from the alternator to the regulator.

 

it would be 3 wires if you were running the charging circuit through the horn relay like Chevy did, but I am assuming for the moment you are doing the charging circuit (big wire) the modern way.

 

The four wires are as follows:

 

1) Ground. Bolt it to the alternator case (there's an empty screw hole on the back somewhere intended for this). Put a big ring terminal on the other end and attach it to one of the bolts holding the regulator to the truck.

 

2) Field. This is the regulator's control wire. It is blue on my truck. It connects to the F terminal on the regulator. On my alternator it connects to the spade furthest from the large post. It is probably marked F at the alternator end too, not sure about that.

 

3) Stator. This is hot when the alternator is turning. It is a white wire on my truck. It runs from terminal 2 on the regulator (right next to "F) to the other spade on the alternator.

 

4) 12v Hot. This would normally come from the horn relay. It is just battery hot. Drop another ring terminal over the big hot post on the back of the alternator. Connect it to terminal 3 at the regulator end.

 

Wow thank you for detailing this out! I have a few questions.
 

The new wiring harness has 12v Hot coming from my starter. With using what you described in your post that 12v should go the the big red post on my alternator and then to terminal 3 on the regulator? 
 

 

[Bloo]

Yes. 12v to terminal 3.