Ask the Mechanic

Tachometer Malfunction

(Photo illustration by Barry Falkner)

READER: I have a John Deere 4600 tractor, and the dash tachometer suddenly stopped working. Do you know if it has its own fuse? Where does it get its power?

STEVE: The tachometer on this tractor gets its feed from the alternator. I bet if you check your alternator, it's no longer charging, which will shut down the tachometer. The voltage in your battery with the engine running will be around 14 volts. If the alternator is charging, the problem is probably in the cluster, which is the complete dash. However, you could have a wiring problem in the wiring harness from the alternator to the cluster.


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