Electrical problem with 87 Cherokee

I'll try and describe this problem as detailed as possible.
Everything was working well for awhile (had the same problem before but it went away) I hit a pothole and my voltage gauge dropped way down. Now I have a variety of issues, including poor performance due to low voltage I'm guessing.

Some symptoms are:

1. After start up voltage shows normal but drops as soon as I put the car in reverse this will also cut out the radio. If I turn key to ON position it'll show low voltage.
2. Radio will cut out when brake pressure is applied (switch activated)
3. Turn signals won't work or blink very slowly but work fine when in PARK (radio cuts in and out with the blinking while in PARK). Will blink slowly if I turn on other items like headlights fan etc.
4. I was rocking the car while the engine was off and the radio on and by rocking the car it would cut the radio out . It didn't do that to me this morning though...
5. When key in ON position and radio on if I hope the rear door (or push dome light switch in door frame) the voltage drops and the radio cuts out then comes back on.

Any suggestions would be appreciated as it's driving me nuts trying to figure this out. I was thinking maybe it's a ground wire but not sure where to look. I think it is related to the lights ...somehow :confused:

Thats a tough one, but I suspect its your body ground wire.

Clean up the negative terminal for your battery. Trace where the neg wire goes to, usually the engine, unbolt it, clean it up with a wire brush and bolt it back up.
Add a ground wire from the battery negative terminal to the body of the car. Just attach it to any clean patch of metal under the hood on the body/chassis. Use 10 gauge wire or better.