1993 Dodge W350 manual conversion with an auto PCM. I'm trying to get my tachometer to read. The PCM was bad so I exchanged with my working one in my truck. CPS is working properly, ac compressor works and battery charges, but the signal does not get to the gauge. I replaced the tach with an isspro tach including the wire harness for it from Genos. What other wires may affect the signal to and from the PCM?

 

Explain a little better.

The truck has an auto harness with a manual PCM?????????

 

Think he did a manual trans swap. So it's a manual shift now, but still running the automatic PCM.

Do you have a FSM? If you do then check the pin out on the main bulkhead wire connector coming out of the PCM for the tach signal. If the signal exists there, then you have a broken wire, or bad connection at some point.

 

I would say bad connection on your wires some where . I have done a manual swap on a truck and used the auto PCM and everything work's Just fine .

 

Isspro is to blame. The tach is a standard EV series, bubble face glass. We read that the older flat face Isspro tachs need capacitor on the signal wire. The newer bubble face gauges have the capacitor within the gauge so a wire straight to the factory plug is all that's needed. I was running the white wire instead of the yellow wire for Isspro's wire harness. Problem solved!