I am trying to get my tach to work with my diesel swap. I have used a prox sensor to trigger a relay to pulse a +12 signal to the black wire comming out of the ignition modual on the fender. No workie.

The original gauge cluster was from a basic guage package, just speedo and dumby lights. There was only 1 wire that was missing from this harness so I hooked one up to it. I tryed on this wire with still no luck.

My other guages are working so it is not a fuse, I don't think? What am I not doing right....................

 

As I understand it a tach signal is a digital signal and possibly AC also. Using an analog prox won't give you what you are after. Why not rob the parts from a distributor and use it as you are using the prox. sensor. Then there would be no doubt on getting the right signal.