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Old 04-19-2017, 06:58 PM   #1
Afirehawk1
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66 C10 Instrument Gauge Testing

Any experience how to test the ammeter, temp, oil and fuel gauges to ensure proper working order while not in the vehicle?
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Old 04-19-2017, 07:54 PM   #2
PGSigns
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Re: 66 C10 Instrument Gauge Testing

First thing I do is put volt meter on each of the electrical gauges and see if they are good that way first. On the ammeters I look the coils for signs of heat if they look dark they are not any good. I have a box that supplies 12 volts and a variable resistor that is between the gauge tap and ground that can test the fuel and temp. An adapter and regulator can be used to air check the oil pressure gauge. I run all the speedometers with a drill after servicing and lubing the heads.
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Old 04-19-2017, 07:59 PM   #3
ray_mcavoy
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Re: 66 C10 Instrument Gauge Testing

The temperature and fuel gauges can be tested by hooking them up to a 12V battery or 12V DC power supply. Connect the cluster case to ground. And use a small (5A or so) fuse in the positive lead connected to the pink wire on the gauge. Or if you don't have the cluster harness in place, the positive lead goes to the terminal on the right when viewing the back of the cluster.

Then connect a test resistor (to simulate a sending unit) between the gauge's sending unit terminal and ground. The sending unit terminals are the ones on the left side of the gauge when viewed from the back (tan wire for fuel sender and dark green for temp sender).

Substituting a 30Ω resistor for the fuel sending unit should give a full reading. Similarly, a 15Ω resistor should give a half tank reading. And 0Ω (connecting the sending unit terminal to ground) should make the gauge read empty.

For the temp gauge, a resistor around 50 to 60Ω should give a hot reading. Something around 80 to 90Ω should read about mid scale. And 250Ω or higher should read cold.


The ammeter is only capable of reading about 1.5 to 2 Amps full scale when it is used without it's external shunt. As a side note, shunt is actually just the section of wire that runs from the power distribution junction on the horn relay over to the positive battery terminal. But to test the meter itself (without the shunt), you can use a multimeter to measure the resistance between the ammeter's two terminals. You should get a very low reading of about 0.2 to 0.1Ω ... might even show zero on some mulitmeters. Another quick and easy test is to hook a small AA or AAA cell battery across the ammeter's terminals. That will make it's needle deflect pretty much full scale in one direction. Reversing the connections should make the needle go the other way. Keep the duration of this test fairly short (don't leave it hooked up for longer than necessary).


To test the mechanical oil pressure gauge, you can hook it up to a source of compressed air through an adjustable pressure regulator. You will also need another known accurate pressure gauge to measure the air pressure. 30PSI should give a mid scale reading and 60PSI should be full scale.
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Old Today, 03:17 PM   #4
Afirehawk1
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Re: 66 C10 Instrument Gauge Testing

thanks for the advice. will start with the voltmeter and see what i can figure out.
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