#1 sounds like carb issues. Have you taken them off and cleaned 'em/ checked them out? A bike that old may have sat for awhile, or have sticking parts, clogged jets, dried/ rotted seals or gaskets, etc. Don't ride with a sticking throttle. Does it idle fine? Is there a lag when you twist the throttle? Does it rev and drop okay when its not under a load, but under load doesn't want to move? Electrical gremlins suck, but you've got a good start. Since you have a new harness, jump on ebay and grab a new/ used light switch. The brake lights should be easy. Check the bulb first, then check for voltage at the bulb socket when you pull the brake lever or press the rear brake lever. Small switch on your front lever perch to activate the brake light from there, and check the spring assembly/ housing at the rear brake pedal for that switch. How old is your battery? May be pooched.