[VetteVet]

To troubleshoot the charging system start with the regulator plug. Pull the plug off the regulator and test the brown wire on the end of the plug. It should read zero ohms with the key off and 12 volts with the key on. The red wire in the plug should have 12 volts on it key on or key off.

Plug the regulator back in and test the small plug on the alternator the same way. pull it out and look for 12 volts on the white wire key on and zero with the key off. The blue wire should be hot all the time. If the points in the regulator stick together it will keep the regulator coil energized and send power to the alternator even with the key off and the alternator will feet warm.

Now pull the large red wire off the alternator and do an ohms check between the large terminal and the body of the alternator. You should get near zero ohms in one direction and a large reading the other way when you reverse the leads.
If you get low lohms both ways then one of the diodes is shorted and allowing battery current to flow through the alternator windings to ground. This would cause the alternator to feel warm to the touch with the key off and it would also drain the battery.

Another good test is to connect a test light between the negative battery cable and the negative battery terminal. With the multimeter on amps, you need at least a 10 amp setting on the meter. With the key off look for a draw greater than .003 or 3MA. That's milliamps. You will probable see 1 or 2 amps if the diode is blown.

Then pull the regulator plug and see if the reading gets less than 2MA. If it stays high then pull the small plug off the alternator. Then if no change pull the large battery wire of the alternator and if you have a blown diode your in the field windings the meter will drop to .002 or less.

The diodes can fail two ways. They can conduct current both ways and the alternator may continue to function as normal except it will drain battery current to ground and drain the battery. This may get a pass reading from O'reillys but the alternator is still bad.

It can also fail by not conducting current either way which is the way most of them fail.

If your readings do not pass and you decide to get a new alternator or regulator, then consider converting to an SI or /cs style and improve you charging performance greatly.

We can walk you through the conversion since it is easy.