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Some instrument panel gauges are not working, what could be the issue?

1996 - Peterbilt 379

The only gauges working are: manifold pressure, oil pressure, water temperature, and air pressure.

Gauges not working are: alternator, fuel guage, speedometer, pyrometer, tacometer, and engine oil temperature.

I have checked the accessory relay and it seems to be working fine (according to test light). What else might I be able to check to get these gauges working?

The gauges have ground but no power.

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Guages work when the truck is started but the alternator wire is removed. As soon as I reconnect the alternator wire fuse blows!!

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Those gauges you mentioned all are hooked up direct. The others are wired electrically, so the dash is not getting power. Did you test the wires at the plug for each gauge? Did you check the fuses?

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Fuel gauge and oil temp can be checked by grounding the wire at the sending unit with the key on, if the gauge pegs out it's the sending unit. Speedometer and tach need to check the sensor pick up at the back of the tranny and in the engine bell housing. Pete Tachs are bad about going out. I can press on my dash and make mine stop and go. Pyro....check the lead wire from the thermo couple to the gauge to check for wire breaks probably the thermo couple. Voltage gauge check with a multimeter at the back of the gauge.

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Thank you for your help! Is there any way that you could give me a call so I could speak with you personally about this situation? If you could call me, my number is: (804)436-6208. Thank you again!

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Jason will be eternally grateful.
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