Was curious if any one knows the location of the fuel sending unit ground wire is that comes from the tank up to the gage. I want to make sure that the ground is well Grounded and not the Sending unit it self. Can have a full tank of gas but the needle will move just very slightly from E so its getting some power but would like it to be just more of a ground issue and not a sending unit issue

 

Do you have in-tank fuel pumps? The ground for the sender is a wire on one end of the fuel pump/sender connector. Basically, this wire is from the harness is connected to a pin on the pump assembly that is riveted to the 'structure' of the hanger. If you don't have in-tank fuel pumps, I'm sure it's much the same as far as the circuit goes, just without the two additional wires to run the fuel pump. You could pull the connector going to your fuel sender, turn the ignition on, and probe with a meter. On a two wire setup (no in-tank pump), you'll have one wite with +5V, and the other it your ground. To locate the ground on the four wire connector with in-tank pumps, take the connector in hand with the ignition on (you may have to jumper it to stay on at the diagnostic connector), you'll find that the two center wires will have +12V and +5V, with the outside wire adjacent to the 5V lead being the sender ground. You could tap into that for an auxiliary pathway to ground for troubleshooting.

 

I am not positive about this, but it might run all the way up front to the driver's side corner radiator support. There are several splices and connectors shown in the diagram, and then they show it going through a front lighting connector. I am only guessing after that, if someone has the official good factory diagrams, it should have a ground location chart on it.

 

Franklin, I think that ground is the one on the inside of the firewall (gotta love the engineering in these trucks). If he has in-tank pumps and has replaced the entire unit, he probably no longer has an external ground. Ford used 4 pins on these, pump power, pump ground, gauge signal, and gauge ground. The gauge ground pin looks like the others, but instead of insulated washers it has a metal pair, aftermarket replacements have a pair of insulted washers so the only ground for the sender is the tank body. If you do not have some kind of ground strap on the tank, the sender won't work.

On a 1980-89 truck the gauge will read empty or below empty, on a 1990-96/7, it will read above full.

 

I wasn't sure when they changed the gauge operation around, I thought it was when they changed the body style, but was corrected and someone said that 87 was still the old style and 88-up was the new. I am still not sure, but do know my 89 has the newer style sending unit and gauges that operate backwards and with different senders than the older trucks.

While I was looking this up, I did look at a newer fuel injected gauge system, and that sending unit used the same ground that the in-tank pump used.

 

Yes, Dave, they are tied together in the harness, one is orange, the other is black. The problem is the pin on the tank module is no longer connected to anything at the tank end. Maybe a Motorcraft one might be, but even NAPA units aren't. It may be the 89 is the newer, I know I had an 88 cluster I was going to use until I decided on the later dash and it worked fine with the 86 senders.

I had to add a ground strap on both tanks for the 90 pump modules to work the fuel gauge correctly.