How to diagnose an external regulated alternator?

My 64 Scout is not charging. It does have the same delco externally regulated alternator (generator?) that GM used. I'm just completing a full frame off resto on the Scout and upon the initial fire up its not charging. I am fully intending to keep it original, so no upgrade to the modern alternator.

I have no idea how to diagnose this system.

Here's what I know. It all worked fine before the resto.

The regulator was new when I bought it. The original was found wedged in the wheel well. I did glass bead the original delco cover and put it on the repop regulator to make it look more original.

The alternator/generator case had an oblonged hole so I took that apart and swapped the case half. No issues or drama during that. I also blasted the case halves.

I have 12 volts at the big stud and the alternator is grounded

The gen light on the dash comes on but doesn't stay on.

Revving the engine produces zero change in voltage.

I had the harness out of the Scout completely. There is some chance a wire broke. Its not in terrible shape but it is nearly 60 years old.

There must be a method to measure voltage at the regulator and run a jumper wire somewhere to kick start the alternator or verify which component failed.. any help is appreciated. I have a moldy Chilton's manual from the 70s somewhere if all else fails!

Thanks

 

Thanks Larry. I'll print that out and give it hell.

 

Going from memory, with the engine running you should have voltage on one of the wires (blue on our Buicks?) at the alternator. The amount of voltage depends on the regulator, which depends on the battery state of charge.

If you have zero volts on the field wire at the alternator, you can “full field” the alternator by unplugging the regulator and jumping the “field” wire to terminal “3” (1 to 3 IIRC). The engine will bog down providing that the alternator and wiring is good, and that you have proper voltage at “3”.

If “full-fielding” the alternator works, either you have a dirty/bad connection at the regulator, or a bad regulator. I think.

 

Thanks, Bob.

 

Disconnect the small plug at the back of the alternator. This is the plug to the brush assembly. Find the "F" or field terminal on the alternator.

Put your test leads from your voltmeter on the battery to measure the battery voltage. You should read about 12v. Leave them connected.

Connect another lead from the positive side of the battery. Use another test lead if you have one. You can use any wire, but you need a small pin connector at the end for the next step. (Keep the free end from touching anything)

Start the car.

Touch the free end of the test lead connected to the plus side of the battery to the F terminal on the alternator. This will apply a full 12 v to the field coil. On the voltmeter, you should see the voltage on the battery immediately start going up as the alternator starts to charge the battery. This is the careful part as it it not easy to do, especially if you have AC....

As soon as you see the voltage going up, remove the lead from the F terminal. You can do it again to verify, but don't keep the lead on too long as the voltage will keep going up. Try not to touch anything else.

This will tell you if the alternator is working.

Also, with the engine off, you can touch the same test lead to the R terminal on the plug to the regulator and hear the ignition coil in the regulator click. This will tell you if that's working. Don't try this if the regulator is solid state....

Reconnect the plug to the alternator and you are done.
'

 

Well I got it charging. I had my power probe on it. I found the "F" terminal on the back of the alternator. It had no power according to the probe. I applied battery voltage and the alternator came to life. Voltage climbed to 14.0. I did some investigation and unplugged the voltage regulator. I noticed the number one tang had deflected when I plugged it in and was not making any contact. The regulator is tucked up in the core support at a funny angle. I bent it back, plugged it in and it is now charging.

Dumb mistake on my part, but at least it was a cheap fix!

Thanks for the help. Normally I'd just upgrade to the 12si alternator and not look back..

 

The modern replacements (even US made) for those regulators are dicey. If your reg fails, but the thin chinese made one with the circuit board in it and swap covers.
Patrick