Ford 340B Instrument Issues

[whit5904]

I have a 1985 Ford 340B Industrial. When the tractor isn't running the fuel and temp gauges appear to be working normally. However when you crank it up the fuel gauge reads full with a half tank and the temp gauge moves up to the red after a few minutes of running. You can unplug the alternator wire and they appear to operate normally. I checked the voltage to the temp sending unit and it reads 12 volts when the tractor isn't running and 7.2 volts when it is running. The parts diagram shows a voltage stabilizer on the rear of the instrument cluster but there isn't one there. Any help would be appreciated.

 

[RickB]

You probably have a bad ground connection at the cluster or alternator. Check the black wire at each component and check the wire for an open or short to 12v. The cluster and senders changed about 1982 and the voltage stabilizer was discontinued then.