94 regal electrical probs

at a loss here and mechanics tell me I'm dilusional...started giving me probs about 8 months ago. found that the wires for the oil gauge were fried, replaced them. the oil gauge works fine but ever since i have been having other probs. the volt gauge fluxuates spiratically, sometimes dropping so low, the accessories shut off and the car almost dies but if i turn the lights on the needle jumps back to normal (12-14)
or sometimes just the opposite, the needle reads normal and with a flick of the lights the need drops drastically. battery and alternator are brand new (8/13), check all ground wires, cleaned connection and terminals, checked wires and bolts on starter, checked the wiring for all the lights including the fog lamps, all solid/no corrosion - all good...sometimes the car wont start, no click...nothing...but keep turning the key eventually she'll fire up (only happens when car is parked on a decline)...then i thought it might be the aftermarket stereo system (deck, amp, subs) causing the problem - disconnected everything, no dice...checked all fuses and relays...good. I am not an electrical expert here so what have i missed, what else can i check?
it seems like the regal is notorious for electrical problems. any suggestion would be greatly appreciated.