1972 chevy c10 alternator problem

[Yeahsmitty]

I recently purchased a 1972 chevy c10 fleetside longbed truck. I have been having nothing but problems trying to get it to run correctly. I'm trying to tackle a charging/alternator problem. It has a 307ci (not the original) engine in it and has had the wiring converted (not so well) to run an internal voltage regulator. I have tried wiring diagram and wiring diagram with no luck to solving my problem. The alternator gets really hot (not while running) and drains the battery. I am attaching pictures to see if I have something wired incorrectly. I'm stumped.

[VetteVet]

: welcome2:

Well first off let me welcome you to the forum. You won't find a better place to find out about the old chevy/GMC trucks.

It's hard to tell for sure but that alternator appears to be an externally regulated one. I think the terminal letters say R and F which are the same as the externally regulated ones. The SI internally regulated ones say 1 and 2 on the terminals.

Your description of the problem could be caused by jumping the field terminal (F) to the hot wire on the back of the alternator. That would cause the field to be hot all the time and drain the battery even with the key off.

The case on the 70 71 AND 72 alternators looks very similar to the SI alternators on 75 and later models. Compare the terminals on the alternators. The internally regulated ones run like this --- --- and the older externally regulated ones run vertical with the case, like this I I .

Here's a picture of the 10 and 12 SI alternators,











Here's the internally regulated 12 SI. the earlier ones were 10 SI and looked like the one in your picture.

You can see how it is wired in this picture.



This is the 69 and earlier models.

You have some creative wiring there which you need to back trace. Especially on the blue/red/white one.

[Wrenchbender Ret]

You have an external regulated alt. The field is hooked up to the hot wire. Like the Vet says it will put a constant drain on the bat. You need an external regulated alt. & wire it according to the diagram.

[RichardJ]

That IS NOT an externally regulated alternator. That is a 10 SI.

The brush holder for the 10DN Ex alternator includes the terminals and they point directly to the rear of the alternator.


The voltage regulator for the 10 SI and 12 SI include the terminals and they point out to the side of the alternator.


Early 10SI cases had R and F, and should be ignored.

[Already Gone]

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[Yeahsmitty]

Alright so I'm confused. I've had 2 people tell me it's internally and 1 person tell me it's externally. I went out and bought an external voltage regulator just in case.

[leftybass209]

Unless you have a very special alternator that has been rewired, you do have an internally regulated alternator. You need to grab a multimeter, and travel that poor wiring out. It will take time, and patience. Just by looking at it, I couldn't say it's jumped to the battery terminal on the alternator wrong or whatever.

Study the schematics so you know what wires should go where, then trace yours out.

[Yeahsmitty]

I guess I should've added this part...I ran the truck today (how it is currently wired) and it tried to melt the wires....I'm going to guess it isn't internally regulated by that

[VetteVet]

Originally Posted by Yeahsmitty

I guess I should've added this part...I ran the truck today (how it is currently wired) and it tried to melt the wires....I'm going to guess it isn't internally regulated by that

I would have advised you to buy an alternator for a mid 80s truck or car with the large ports in it like the one in my picture above, the 12 SI . Then you could wire it yourself with our help.

You may have already smoked the alternator you have so you may have to buy a new one.

Which way were the terminals running on your present alternator? See RichardJ's
post and my first one above.

[Yeahsmitty]

My posts run ||.

[VetteVet]

External --- What's your plan?

check this out.----http://67-72chevytrucks.com/vboard/showthread.php?t=417872

[Yeahsmitty]

I'm going to take back the alternator I have and get one with an internal regulator. It will be the easiest route.

[dflarsen77]

Looked at an alternator on Autozone's website from an 85 c1500 and it has the plug like Smitty's, with the R and the F, but it has the 1 & 2 on there also, above them. On Smitty's pic, you can see the 1, but the 2 is hidden by wire.



Man, wiring problems suck when you buy one of these, because almost 50 years worth of dudes have screwed with them...

If it's hot all the time like he says, and those other problems like wires melting, how would the alternator cause that? I would think the alt was fine and it's just something in the way the conversion down where the volt reg used to go was done wrong. I still don't see how though.

[VetteVet]

Originally Posted by dflarsen77

Looked at an alternator on Autozone's website from an 85 c1500 and it has the plug like Smitty's, with the R and the F, but it has the 1 & 2 on there also, above them. On Smitty's pic, you can see the 1, but the 2 is hidden by wire.



Man, wiring problems suck when you buy one of these, because almost 50 years worth of dudes have screwed with them...

If it's hot all the time like he says, and those other problems like wires melting, how would the alternator cause that? I would think the alt was fine and it's just something in the way the conversion down where the volt reg used to go was done wrong. I still don't see how though.

When you have an externally regulated alternator, the regulator controls the voltage going to the alternator fields by shutting the voltage off and on. This keeps the alternator from getting a constant 12 volts all the time.

In his case he has an externally regulated alternator without the regulator and the previous owner wired it up like an internally regulated unit. This means he is getting a full 12 volts to the fields which will make the alternator put out full amperage whenever the engine is running which will over charge the battery and overheat the wiring. With the engine not running it drains the battery just like leaving the lights on.

he may also have one or more shorted diodes in the alternator which creates a direct short to ground from positive to negative that will burn up the wires.

He's going to get an internally regulated alternator and we'll help him wire it up and it will solve that problem.

[VetteVet]

Originally Posted by Yeahsmitty

I'm going to take back the alternator I have and get one with an internal regulator. It will be the easiest route.

Get the 12 SI with the bigger ports in the back for better cooling. I think the 86 and up trucks used them. If you wanted to go even newer to the CS style you can, but you'd have to change the drive pulley and add a resistor in the exciter wire, or get an adapter with the resistor already wired in.