Just an educated guess - sounds like a loose connection somewhere.
Trouble shooting 101 - did it ever work right? If so, go back to that configuration and get it working like that again. Then, change one thing at a time until the trouble symptoms appear.
Electrical troubles can be tough. Old wires get brittle, insulation cracks, connectors corrode, splices fail and so on. Often, previous owners have altered the wiring in - shall we say - unconventional ways.
Pantera place has good electrical info and diagrams at http://www.panteraplace.com/page107.htm
Good luck; ask away if you need more assistance.
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