How does the fuel sending sending unit sent the signal to fuel guage on a 71 dart.

The ignition switch sends 12V to the cluster, and powers the voltage limiter (regulator) for the temp/ fuel gauge, and oil gauge if you have one Power goes through the gauge, and the sender terminal of the gauge goes down the dash harness to the connector in the left kick panel, where the rear harness goes under the sill and to the rear of the car. The sender wire hooks to the sender, which changes resistance according to fuel level, and ground.

First determine for sure that the temp gauge is working. This will show that the voltage limiter is working, which supplies both gauges

Then ground the sender wire, and turn on the key, watching the fuel gauge. Don't leave the key on longer than it takes to observe the gauge. It should quickly head for "full."

If this works, go back and check the sender with an ohmeter. Approximate resistances are:

L = 73.7 Ohms (empty)
M = 23.0 Ohms (1/2)
H = 10.2 Ohms (full)

Factory cars came with a little clip on the sender tube which jumpered from the sender tube, over the length of the rubber connector hose, and clipped to the fuel line. If this is missing, devise a ground. One way is to take a fuel line clamp, scrape the sender tube clean, and wrap some clean stripped wire around the tube, then clamp it with the hose clamp. Run the other end of the wire to a bolt on the body.

If the sender resistance seems OK at the sender, hook up the wire and re--check at the connector in the kick panel. If that seems OK, time to pull the cluster

Some problems at the cluster include---


Bad instrument voltage limiter or bad "socket" connections where it mounts

Bad connections at the PC board harness connector, loose corroded connector pins

Bad connections at the gauge, loosen/ tighten the nuts a few times to "scrub" the connection clean

Of course the gauge unit, or the sender, depending on test results, can also be bad.