I have been sitting here waiting for an electrical problem to come along... You don't say what year it is, but I don't have a specific cure for you anyway. However, my years as an electrionic tech taught me that connectors and solder joints are the root of all evil. And when you have an imperfect crimp, a connection that has gone bad for some reason (corrosion, heat etc), or a bad solder joint, these things can be very heat sensitive. And sometimes they take years to appear. Considering the miles of wires in a car (OK maybe not miles) and the hundreds of connectors/connections (several hundreds), there are lots of opportunities for trouble. It could take a trained electronic tech with a schematic quite a while to find the trouble. Hopefully, with a schematic, you can look at the symptoms and see what might cause these problems, but it might be a long shopping list. The key to fixing something is recreating the fault and this can be hard to do. The wiggle test sometimes helps as does tapping on suspected bad connections. Hopefully some one out there has had the same trouble and can point you in a specific direction.

Mike

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra