[Shamu406]

Can anyone shed light on why my (VDO) RPM gauge may not be working?
My Pro Driver has not worked for over a year, but not needed so much. 
Tommy at Newell said to check fuses under passenger dash and connections behind the gauge. 
Thanks!

[77newell]

There are four things required for proper operation: 1) 12vdc supply, 2) ground connection, 3) signal from alternator (probable source), 4) the gauges internal circuits are working.

I would check the connections on the back of the instrument to make sure they are all connected and then verify voltage and grounds. If those are OK then check for voltage on the signal wire with engine running. If this checks OK, replace the gauge.

[Shamu406]

Thank you John, I will try those!
But I was told the signal comes from the DDEC ECM on the side of the Detroit 60 Series engine.

[77newell]

It may come from there, but in any case the gauge requires a pulsing voltage to operate. It's a signal I would expect to be able to detect as voltage though not the pulsing with a VOM.