[Richard]

That is helpful info.

That is a Penn Tex alternator. And you have the belt setup that is prone to slippage.

With the dropping voltage, you definitely are NOT getting amps/volts to the batteries. There can be a number of reasons, we just have to figure what the issue may be. https://www.qualitypowerauto.com/Penntex...lyl_VBEcr7

This may get a little hairy, because I found on my 95 with the same setup, that Newell wired it a little differently, and they used a different voltage regulator.

Let’s divide the problem into three areas of root cause;
The alternator is not putting out the correct voltage/amperage
The voltage regulator is not putting out the correct signal to the alternator.
The cabling, or isolator, is not allowing the voltage to reach the batteries.


I don’t know how comfortable you are with a voltmeter and diagnosing the issue.

The next easy step as Jeff suggested is remove the alternator and take it to a shop. You might also take the regulator while going to the shop. The regulator is located inside the stainless cabinet to the right of the engine.