gauge calibration

Does anybody know how to calibrate fuel, temp, oil press. gauge on a 70 b-body rallye cluster. I sent two clusters out and had them totally redone look great but the readings are not right. I can go into greater detail but it is not the voltage limiter or sending units.

The factory tool tester for gauges had three settings, 73 ohm low, 24 ohm midrange, and 10 ohm high. It works for all three gauges. You can rig one up with a power supply and corresponding resistors. The backside of the gauges have small holes that you can reach into with the tip of a penknife blade to tweak the needle. You can test with a 12 volt supply by connecting positive lead to 2nd pin from right, and resistor connected to negative lead. Just touch it to corresponding gauge pin terminal and watch the gauge.
Also- if you installed an aftermarket Gas Sender your Fuel gauge will not read properly- they are built using a linear scale and half tank reading will be approximately 44 ohms instead of 24, so gauge will read about 1/4 tank.

Great response Pynzo!
I'd like to clarify something.

Using those 3 resistors doesn't require a power supply.
For example; just pull the wire off the temperature sending unit, connect an alligator lead to each side of the 10 ohm resistor, the other ends of the alligator leads.....connect one to a good ground like a carb stud and connect the other to the sender wire. Your gauge should now read 100% (with the ignition key on). Allow a couple minutes for the gauge needle to reach 100%.....some are slow.

Then sub in the other 2 resistors for 50 and 0%.
Do the same for oil pressure and fuel. This will give you an quick check of gauge accuracy.

If the gauges are way off, you will probably remove them for bench calibration. A power supply or battery will then be needed to supply 12 volts to the gauge voltage regulator.

Bottom line is to substitute the 3 resistors for the sending units.
To come up with those 3 resistor values you may have to put other value resistors in series or parallel to obtain the correct values. An old trick is to take a carbon comp resistor that reads low, say 70 ohms, and file the center of the resistor to notch it. This filing will increase the resistance.

I had posted this a while back as I have the factory calibration tool so I measured the values.

https://board.moparts.org/ubbthreads/ubbt...tml#Post1789021