Hi There. I'm hoping that someone can help me with an issue that I have. Basically I'm running a programmable 6530 6AL system, the grey tach output wire is connected to the standard rev counter (Rover SD1), the rev counter works correctly until the revs get to 3500 RPM, but at that point the needle drop to zero. With the standard ignition system the rev counter is connected to the positive terminal of the coil (I believe), but I have been told that it uses some sort of 'flyback pulse' from the coil which is around 50V.

Anyway I have tried to fix the problem using the MSD 8920 tach adapter wired up for a voltage triggered rev counter and for a current triggered rev counter, neither method worked, the rev counter did not move at all! The wiring instructions seem a bit unclear for the adapter but for the voltage triggered method I connected the white wire from the 8920 to the grey wire from the MSD, the black was earthed and red was fed +12V, the violet was connected to the input of the rev counter. (The tach adapter did make a buzzing sound while the engine was running.)

For the current triggered method the red wire was connected to the tach input, black was earthed and the grey wire from the ignition system was connected to the white wire of the adapter. I suspect that it might be impossible to get the rev counter to work, but I thought it was work putting a post up just in case anyone as fixed a similar issue.