I've got a problem with the tach in a 91 740. With the engine/ignition off, the needle falls to the 7000 side. When the engine is started, the needle reads a steady 2600 rpm's regardless of the throttle position. In looking over wiring diagrams ( I'm not that great at fault tracing) it appears to me that the tach is connected to the power stage ( regina system) via a red/white wire so it must "read" engine rpm there. I don't see any ground wire anywhere. I've tried cleaning the connection with no luck. Anyone have any ideas? I put on a new power stage unit about a year ago but the tach worked fine after the swap for about 8 months and then quit. Thoughs much appreciated.

jake 183,000 and cookin'