[T E Lewis]

Don,

Take the tach out, the plug that goes into the back of it should be a six prong unit. Take the wire from the #3 position, move to the #4 position, do not reconnect #4 to anything and leave #3 blank This will make it pick up the correct pulse from the MSD. You will probably find that the wire coming out of the #4 spot currently goes to nothing, and is just a short stub in the wiring harness. This will cure your problem.

Thom