Roger Mabry

I have my dash cluster out and would like to test the Voltage Regulator or squirt module located in the upper RH corner of the cluster on the rear. It
slides out when the latch is released.

I am having gas gauge problems with it always being above Full and this has been mentioned as a possible source of the problem - but changing parts without testing them is a waste of money...

But taking out the dash cluster again for not testing the module is not a good thing....

Anyone know how to test it?

dawson1112

Your problem is likely a short to ground in the wiring some where between the sending unit and the gauge.

The float mechanism operates a potentiometer (variable resistor) empty the float is at its lowest this creates a 0 ohm reading or very low resistance the gauge registers this just like an ohm meter would measure ohms open or no resistance = empty. When the tank is full the float is at its highest creating a high resistance.
If your gauge reads way above the full mark this means that there very high or infinite resistance causing the gauge to peg above the full line. A short to ground in the + wire that goes to the sending unit for the gauge will cause infinite resistance .
Removing power by disconnecting the battery will test this. With the battery disconnected the gauge should drop below empty.

Roger Mabry

I have the cluster out now for cleaning, bulbs and a new plastic cover..will check it when I re-install.

Since I was in there now, checking the thing seemed like a good idea...no
matter the problem - a gas gauge is necessary...using the odometer is just
WAG at times....

petrock

While what you said is correct in how a potentiometer works (variable resistance), it is not how the gauge in the instrument cluster works. The gauge doesn’t read ohms (see below for why) it reads current flow (amps). The sending unit (potentiometer) in the fuel tank varies resistance based on the position of the float lever in the fuel tank. Low resistance allows more current to flow and high resistance allows for less current to flow. The fuel gauge reads the amount of current flow (amps) and adjust its needle accordingly. The low end of the ohms scale on the sending unit is not 0 ohms. That would be a short to ground. There has to be some amount of resistance on a circuit, otherwise current would flow unobstructed and all hell would brake loose in the circuit. According to the factory service manuals circuit diagram for my wifey’s ’96 mustang, the range of the sending unit is 22.4 ohms for empty & 145 ohms for full. The voltage on the circuit is a constant battery voltage (12.x volts). So, by applying the equation from ohms law (volts / ohms = amps), where volts is battery voltage (12.6 volts for discussion sake, but your voltage will vary) its .56 amps for empty & 0.08 amps for full.

Measuring ohms on a circuit/component can only be (reliably) done when there is no current/power/amps flowing through it. If there is any current flowing the ohm reading will be way off and could potentially damage your meter. An ohm meter works by sending a fixed amount of volts & amps down one meter lead, through the circuit, and read the amount of volts & amps that appears at the other meter lead. It then applies the equation for Ohms Law (resistance = volts / amps) to determine the amount of resistance in the circuit.

This is also why doing an ohm measurement to determine the health of a circuit is virtually useless, unless you already know what the ohm reading should be ahead of time. To properly check the health/condition of a circuit, you need to have current flowing through it. So it has to be plugged in and turned on. Then use a voltage drop test. If the voltage across the circuit/component drops more then .5 volts, then you know there is a problem with the circuit. If it is below .5 volts, then the circuit is fine. Its that simple.


Kind of. Infinite resistance is a open circuit, which would mean there would be no current flow, which would mean the fuel gauge would read empty. The gauge pegged at or above full means that there is high resistance on the circuit, which would mean there is corroded/damaged/fraid wire or connector somewhere on the circuit, the gauge needle is suck, or the float lever in the tank is stuck in the up position.


That is incorrect. As stated above, infinite resistance is an open circuit. A short to ground does not change the resistance on the circuit (strictly speaking), or create an open in the circuit. It provided an alternate and less resistive path for the current to flow. Current, like water, takes the path of least resistance. With this less resistive path, more current will flow then the circuit was designed for which will cause a fuse to blow (if your luck).


That just tests that the gauge is able to read the current flowing through the circuit. It doesn’t test the fuel tank sending unit or any of the other circuitry involved.

petrock

Oh yeah, the voltage regulator is attached to the alternator.

Roger Mabry

The fuel gauge does move to about 3/4 when the key is off.


When On it moves over Full and stays there...will start checking at the tank and go forward on the wires when the car is back together again. If
needed, will drop the tank and check/change the fuel sender. It will work properly soon...

Will have the new dash parts - dimmer switch and new gauge cluster plastic cover in a couple of days. Then I should have lights in the dash again.

I think I found the problem on the blinking Air Bag light, car was in a front end accident and PO fixed the problem after being paid for the insurance value
and then bought the car back as Salvage. He did the fix "on the cheap" and did not replace the harness and air bag sensors near the headlights...hence
the Air Bag warning light! Will just take out the Air Bag bulb and live with the "beeping" or disconnect the aural warning device...

Am concerned that replacing that harness (cheap to buy) might not fix the problem(s) and might set off the air bag or cause more ... will live without
until the more important problems are resolved.

Need to find a solution on how to replace the vertical rubber seals on the quarter windows, have the new seals but NO ONE KNOWS or is TELLING how to change them...I cannot see how the two metal pieces are attached.

Roger Mabry

With the new dimmer switch, I have now have dash lights and the headlight switch etc is illuminated!

The new plastic gauge cover really makes a difference!

Took out the Air Bag bulb and will remove the connection of the "beeping box" so I not hear the aural warning all the time..

Still have to put the lower stuff back on but that is for another days work. Gas gauge still reads over Full so I will start chasing down that problem while the dash parts are still off the car, just in case...

Bubba 95SN

IVR is on circuit panel for dash. VR is on alt.