Charging issue on 1990 244

Hi, I have 1990 244, auto, having a charging issue, have been through the following, started with replacing the battery as it tested bad, wildly fluctuating voltage. Did not fix the problem, then replaced the Alternator with a known good one tested in running parts car, also replace the ground wire as it looked iffy, still not charging, replace bushing on bracket as it was totally collapsed, still not the solution. Tested every single fuse, wire, etc, and have found two things, the alt light in the dash does not work (My Bentley says if this circuit is not lighting up, im not going to get charge action) have traced every wire having to do with circuit, as well as the alternator, and found there is a short between engine compartment and alternator, tracing every wire, thinking it may be big plug at back of engine, i have heard of these going on the earlier cars, has anyone else experienced this, getting a little-frustrated want to drive the car before snow flies, if anyone has other suggestions
. Thanks TB

It seems like you have figured it out but are not listening to the symptom. You wrote your dash light is off. The manual told you if that light is off you get no charging. So your next step is to test that charge light circuit.

The charge light can be tested by disconnecting the wire from the back of the alternator. Then you can connect the wire to the alternator case. Ground it to the case. With the key turned to on the dash light should be on. If the light isn't coming on and you have a good grounded alternator case. Then you need to remove the cluster and check/replace the bulb.

You may also need to clean or replace fuse 12 as that provides power to the charge light in the cluster. Without good power the circuit with the bulb won't excite the alternator to charge.

Oh and the alternator wiring can decay where it goes under the crankshaft pulley and toward the alternator and wiring does decay at the big gray plugs at the rear of the engine.