Instrument voltage reducer

[rsrose]

Does the 1962 GMC 1000 Series have one or two Instrument Voltage Reducers on the back side of the original instrument cluster? This part, if it exists, is also called an Instrument Voltage Limiter or a CVR (Constant Voltage Regulator). Again, if they exist, who has them?

[James]

The 1962 manual does not show any voltage reducer(s) for the instrument panel or anywhere on the truck.

What is the problem are you having?

[rsrose]

New sending unit in gas tank, grounded correctly, but gas gauge always shows 3/4 full even with the tank empty or full.

[James]

Let do some basic troubleshooting. Disconnect the wire from the sending unit. With the wire disconnected, what does the gauge reads? Then place the wire directly to ground, what does the gauge reads?

[rsrose]

James,
Disconnecting the wire from the post of the sending unit, the gas gauge needle goes all the way to the right, or to full.

Touching the wire to the ground sends the needle all the way to the left, or to empty.

[AZKen]

Sounds like it passed those tests, so next question: What does needle do when ignition is OFF?
You can have a stuck float, stuck needle, bad sender or bad gauge.

Also: Why are you just now noticing that? What have you done wiring wise and what have you replaced recently? Please give part numbers and vendor name of any parts recently replaced. Give description of any work/wiring done.

1. Sending units are not voltage specific but require correct ohmage.
2. Gauge is voltage and ohm specific.

[James]

Originally Posted by rsrose

James,
Disconnecting the wire from the post of the sending unit, the gas gauge needle goes all the way to the right, or to full.

Touching the wire to the ground sends the needle all the way to the left, or to empty.

Sound like a stuck/bad sending unit.
Next test is to remove the sending unit from the gas tank. Connect the wire back into the sending unit stud. With a jumper wire connect one end to the base of the sending unit and the other to a good ground. Next you should be able to slowly move the float up and down while watching the gauge. The gauge should follow the float movement.

While moving the float slowly it should move freely. If there is any sticking along the way, the sending unit is bad. If the gauge do not follow the float movement, sending unit is bad.

[FetchMeAPepsi]

Not to muddy the waters, but IIRC my Oreillys sending unit maxed out at 3/4 tank too and I had to install a grounding wire or a resistor on the line to get the new one to act right.
I can't remember which right now though.

To test that out, I pulled the sending unit again and just ran it up and down by hand, watching where it maxed out.