Tail light schematics?
 

My right tail light is much dimmer than the right; when I brake, the right tail light dims completely and the left tail light brightens up as it should.

Sure enough, it happened after some heavy rain. I also noticed the dash lights and headlights flicker along with the engine speed at idle. Is this bad plug wires or alternator issue?

Anyone know where I can find wiring schematics? Already got pulled over leaving the bars (wasn't drunk enough, thankfully).

seals around the taillights are known to leak.. could have some water in there causing a short.. Peal it off dry it out.. Did you perhaps change the bulb? You have power so its a voltage issue..

as for flickering lights id check your alt first.

Yes, I changed the bulb, nothing changed. I think I'll just take the whole thing apart and see what I find.

I had a similar problem with my '88. One bulb was dimmer than the other four for both the tail light and brake light. After looking at the tail lights and the wire connections, I noticed the grounding wire, screwed together with the bulb holder, was corroded. I sanded the corrosion off both the bulb holder lug and wire connector, then re-assembled it with plenty of dielectric grease on the lug and connector. It's been good for two years now.

good stuff.. probably the issue