A big +1 on a FSM. It'll make EVERYTHING easier on your project. I'm not much on electrisicals either, but our cars have a rep for at least as many (or even More) shorts as any others. Maybe run out every time the temp changes drastically and measure to see if it's something variable/intermittent. Can relays stick partway? The reason I think of all this is an '80 Riv (the flimsy metal sheets with the rotting foam separator contact type design) that blasted the horn at 2AM going into Fall when it started frosting.
Also, get a friend to wiggle TS outta the wiring everywhere (even take out the seats and get a stick to poke under the dash) while you're measuring.
\'96SS SOB: SSRI, Herter Tune, Tri-Y II, , 3000 Edge, F/HO bars, METCO extendeds with CV MMC, Bilsteins, currently Vredestein Ultrac Sessanta (315/35 rear)
\'96FWB BUW-Butt Ugly White: PCMPerformance tune, HDFA w/ swissed filter, 1/2 SLP s.s. catback with H- and Flow Super 50s, oem opti rebuilt 3 times, SS Bars, METCO LCA, Airlift 1000, Monroe SS, PowerTrax No-Slip, CTS wheels with +1 rubber. Finally, wait for it... LT-4 knock module!