Intermittent Charging Problem

My Significant Other just gifted me an '86 Power Ram that she's had for years. I had to put a battery in it, and I noticed the OIL and BATT idiot lights didn't come on with the key (no gauges yet) but it started right up and ran fine, with BATT light ON. I pulled the "T" connector from the alternator, along with the blade connectors in the "feeder" wire from the + cable terminal, flushed everything with WD-40, connected/disconnected everything a few times, then hooked everything back up. PROBLEM SOLVED! Idjit lights came on with key, engine started/ran fine with NO warning lights. THEN: Next day (today) I loaded the truck for a dump run, and the same problem was back! No OIL/BATT lamps with key "ON", Engine starts fine (so I have good remaining battery voltage) and BATT light stays on when running.
I cleaned the connections once, and thought I'd fixed it. What should I do or check next?

Congrats on getting the truck Maxedoubt ~ I don't have the answers you need but someone here does... I know that the brake warning light comes on if the brake fluid gets low... I had to replace the oil pressure sending unit to extinguish that light... I lived in South Everett over twenty years member FMS88 lives in Seattle and he really knows a lot about these trucks... You could PM him to see if he has the answer...

This might be a dumb question, but have you probed it with a voltmeter at all? Just to verify that the alternator is in fact charging, and that the the alternator voltage is seen at the battery when it is running? The only other thing I could recommend, is visually trace the feeder wire from the alt to the battery, checking bends and connectors carefully. Although it sounds like you've already done that. Mine died on me once because the wire was corroded and broke near that spade connector on the battery side, an easy fix but it took me awhile to figure out what had happened. I never got a charging light on mine though.

NOT a dumb question. The answer is NO, I have not had any time to really get down on it yet. I am confident (not to be confused with sure) that it was charging when the BATT light was out with engine running.
Kinda hoping one of my MR50 brothers would chime in with "Oh yeah, that's real common with these trucks, here's how to fix it forever", or something like that. No such luck so far.