Gas Gauge Help!

[67alldiy]

I know this topic has been discussed quite a bit however I need some confirmation.

My gas gauge is stuck at 1/4 full. Used to work fine until I pulled the dash and replaced a few things. I have checked an re checked everything and need to know.

what exactly does the resistor do on the back of the gas gauge?

should there be voltage coming from the pink wire that feeds the temp gauge and gas gauge when the ignition on? if so should it be 12v?

my gas gauge does not move when I take the wire off the fuse box labeled fuel, it also does not move when I try to ground out the connection on the fuse box, stays at 1/4 full

It also does not move when I ground out the gauge. to do this I connected a temp wire from the center post of the gas gauge to cab. is this correct?

I am at a lost to try to figure out why this would be? Any help would be appreciated.

[ray_mcavoy]

The gas gauge has two electromagnetic coils inside. Current flowing through them creates a magnetic field that acts on a small piece of steel connected to the needle, causing the needle to move. One coil pulls the needle toward the "empty" side of the scale, while the other pulls it toward the "full" side.

The coils are wired in series with one another with the sending unit tied into the common connection point between them. The resistor (on the back of the gauge) is wired in parallel with the "empty" coil so current flow is divided through the two. If the resistor fails open circuit or simply isn't making a good connection, it increases the current flow through the "empty" coil and generally results in a gauge that won't read much over 1/4 even when the tank is full. The gauge will still move though, and go to empty if the tank is empty or the sending unit wire is temporarily grounded (simulating a sending unit at the empty tank position).

Yes, the pink wire that feeds both the temperature and gas gauge should have full battery voltage present when the ignition is switched on.

When you temporarily disconnect the "fuel" wire connection at the fuse box, that should simulate a sending unit in the beyond full position and cause the gauge to peg beyond full. Similarly, temporarily grounding that connection should make the gauge read empty.

The fact that yours is completely inoperative sounds like there might be a bad connection somewhere between the pink wire and the power terminal on the gauge (possibly an issue with the printed circuit on the back of the cluster). Or an internal problem with the gas gauge itself.

The gas gauge normally grounds through the metal cluster case. And it sounds like you've already tried adding a temporary ground wire to rule out a ground problem.

If you have a multimeter, you can test the coils inside the gas gauge to see if one of them is broken or burned out. With the meter set on the resistance (Ohms) scale, and the gauge removed from the cluster, measure between the gauge's +12V power terminal and it's sending unit terminal. You should get a reading somewhere around 85Ω. Similarly, measuring between the gauge's sending unit terminal and it's ground terminal should give a reading of around 100Ω. If you get an infinite (open circuit) reading the gauge is bad. You can also check the resistor by measuring it while it's disconnected from the gauge. It should be around 88Ω.

[TBONE1964]

Originally Posted by 67alldiy

I know this topic has been discussed quite a bit however I need some confirmation.

My gas gauge is stuck at 1/4 full. Used to work fine until I pulled the dash and replaced a few things. I have checked an re checked everything and need to know.

what exactly does the resistor do on the back of the gas gauge?

The resistor is basically a voltage limiter. Not something that is easy to explain.

should there be voltage coming from the pink wire that feeds the temp gauge and gas gauge when the ignition on? if so should it be 12v?

Yes, with key on, the pink wire should have battery voltage.

my gas gauge does not move when I take the wire off the fuse box labeled fuel, it also does not move when I try to ground out the connection on the fuse box, stays at 1/4 full

This is because your resistor is limiting that movement. If the resistor was good, then removing ground or signal wire should move the needle past full.


I am at a lost to try to figure out why this would be? Any help would be appreciated.

Google "the truck and car shop" in Orange CA. They have new resistors.

If you remove the and ohm test it, it should show around 85 or so ohms. You may need to clean the contacts with some steel wool before testing. If you are only reading 1/4 tank no matter what the fuel level is above 1/4 tank, it is typically the resistor that fails.


Hope this helps, let me know if you have any questions,

Tom

[67alldiy]

Thanks so much.

Can you tell me where the pink wire gets its 12v from? It seems I do not have voltage at this terminal.

[TBONE1964]

Originally Posted by 67alldiy

Thanks so much.

Can you tell me where the pink wire gets its 12v from? It seems I do not have voltage at this terminal.

It comes from the ignition switch.

[RustyPile]

Originally Posted by 67alldiy

Thanks so much.

Can you tell me where the pink wire gets its 12v from? It seems I do not have voltage at this terminal.

The number one tool when conducting electrical repairs is a wiring diagram.. If you don't have a diagram, get one.. It shows wire gauge, wire routing, and wire color..

Start with the basics. check for loose or corroded connections, blown fuses, bad or missing grounds.. Pay special attention to the "fingers" on the cluster printed circuit board where the multi wire connector plugs into the cluster. With no movement from the gauge needle, I'd first suspect lose of voltage to the gauge itself..