I've had 3 of those bikes '91.'92, 93and still have the 92. Electrical is usually an issue with the spade terminals in the power distribution panel under the cover to the left of the headlight. I have twice had to pull and individually clean the entire panel and connectors to rectify electrical problems in those bikes. It seems like a common issue and if it sat outside there is a good chance that a few are corroded.
The rear brakes are adjusted with the black knob sticking out of the rear caliper over top of the chain guard on the right side of the bike right beside the recoil. You can feel the pedal come up as you adjust it. It doesn't take much to get brakes back if there is pad left. Remember, the rear brake is a driveline brake and only works when it's in gear. Step on it before shifting and it won't grind into gear ; )
FYI, there is a burp valve on the top of the head that you bleed air from the cooling system with. If you ever get a leak make sure you bleed the air before you run it or you'll melt er down.
This is my '92