Alternator OK? Maybe Regulator??
 

My 66 GMC will go through a period where it won't charge. I check all the wiring and belts, tighten stuff up, etc. to no avail. Then suddenly it will start working again while I'm driving down the road. Not sure if an alternator will perform like this not if it's on it's way out, or if maybe there's something wrong with the voltage regulator. Is there a check/test to see if it's the alternator or what??

Thanks

You can check your alternator if you take it to an auto parts store like auto zone or kragen.

With the engine running, check the voltage on the alternator with a digital volt meter.

Put the dial knob 3 clicks to the left, then put the red tip on the connector on the "F" on the alt, and the black on the ground spot at the voltage regulator.

See what reading you get, then move the red tip to the other tap next to it that the "R", see what reading you get. Then try the same thing on the voltage regulator.

If looking right it, the plug should be at the bottom with 4 tanbs, the far left one if the "F", the second one should be the "R", the third one is "Batt", and the 4th is a return to the guage cluster.

Also while the engine is still running, check the "batt" wire witht eh red tip, and the black at the ground by the voltage regulator, and see if you're getting 14 volts.

Also check the voltage acros the terminals, red on red, and black on the black terminals, and see if you get the same reading as at the alternator. Then turn engine off, and see how low the voltage drops at the battery.

The power should not drop no lower than 12.3 volts at the battery with the engine tuned off. If the voltage regulator needs replacing, I picked up a new voltage regulator for $12 at Autozone. :cool:
David

If a new voltage reg. doesn't fix it, check your grounds. I had this problem last year, and one of the grounds running to the voltage regulator had broken at the firewall connection. It runs in to the starter switch and makes a ground to pull in one of the voltage regulator coils.