[DougD]

Originally Posted by Xavier

Tom I have did all the trouble shooting.

Tach wiring is fine - 3 wires Ground (okay) hot (okay) tach feed (okay)
Had Autometer check out the tach (okay)
DO NOT want to take out the MSD box, a pain in the butt. Can check for 2 to 5v coming from the MSD box to the tach feed (okay) but this can actually read correctly and still be a problem because the true tool you need is an oscilloscope (don't have one).

So, no need for the lesson in trouble shooting - just wanted to know if connecting a tach to the coil while still running a MSD box will do something harmful to the tach. MSD box works otherwise.

I can try it myself to see, but did not want to burn up a good tach trying, or worse yet, something else.

I can't see that working correctly.

MSD = Multiple Spark Discharge. Multiple sparks = multiple tach signals = screwy tach readings. They wouldn't provide a tach signal wire if it was OK to hook it up to the coil.