Tachometer malfunction

[Perry Burney]

I have a 89 classic with a 8V92. My tach malfunctioned, jumped a little and just went to zero. I've had experience with speedometers and oil pressure guages, but not tachs. Where do I start?!

[J Clark]

Tachometer malfunction I apologize for the slow response, but I was attending the Newell rally in Palm Springs. The food and entertainment was fantastic, and Karl and Alice (owners of Newell Coach) were very gracious. Now, to your question, I lost the tach on my '79 Newell (Cummins) twice. The first time was a loose connection and the second time was the sending unit. The most common source of tach failure in descending order are; loose/corroded connection, broken wires, failed sending unit, bad gauge and broken drive shaft. I am not a devotee of remove and replace, nor do I enjoy yoga-under-the-dash or low crawling in the mud. In your front and rear terminal compartments are ?tach? wires (position #16, #6 & #7 on mine). I would first clean and check the connections. Next, place your trusty voltmeter in the ohms position, and put the red lead on one rear terminal (#6 or #7 ?) and ground the other lead. Record the ohms and volt readings on both terminals. Start the engine, you should see a significant increase in resistance (Ohms) and a small increase in volts (10ths) on one of the terminals. If not, stick a brew in the freezer, put on the coveralls and knee-pads, and start tracking the wires down to locate the engine sending unit. There are several places it can be on an 8V92 (blower, camshaft, or alternator driven) and I have yet to check what output Newell Coach is using. Clean and re-attach the connection at the sending unit and try the tach one more time. If a no go, you might free the moths from your billfold (in my case anyway) and order a new sending unit, or remove, inspect and repair everything as needed. Good luck!- jc