[Mark Hislop]

I have had the same problem. In my case, the fix was simple. There are two wires coming out of the mag for the tach. They join the wiring harness through individual spade lug disconnects. In one case, the spade lugs were loose. In another case, one of the wires was almost broken completely through and making contact intermmitantly. Check the wires first before you fool around with the pickup inside the mags.

Mark