I have a '81 Z with a troubled tach. When I turn the ignition switch on (without cranking) the tach goes to 500 rpm. As I watch it, the needle creeps up to about 1200 rpm and seems to stop there. When I crank the engine, the tach needle pops clockwise to the 6 o'clock position. I checked the continuity of every circuit on the printed circuit board. I check the continuity of the brown wire from the circuit board harness to the distributor. I disassembled the distributor to make sure everything looked ok inside. I put a voltmeter on the brown wire pen of the wiring harness and read the voltage from there to the chassis ground when I turned the switch on without cranking and got none. I checked the voltage when I cranked the engine and got about 14.7 DC volts. When I rev the engine, the voltage doesn't seem to move notably. Please help. Thanks.