Here is a procedure I wrote on testing a faulty gas gauge. This goes though testing every component in the system that may help diagnose your issue. Especially read section 6.3
Testing a Gas Gauge on a Stovebolt
Written for a ‘47 thru ‘55 first series, but may work for other years
The steps are as follows:
1. At the sending unit, remove the wire that goes to the gauge. The gauge should go to full. Now touch the wire to a known good ground. (Run a jumper to the battery negative if unsure). The gauge should go to empty. If you pass both of these tests, that tells you that the sending wire and the gauge are OK and the sending unit and/or the ground at the sending unit is the issue. Check sending unit grounds. Clean contact surfaces and/or replace wire and connectors.
2. If your gauge still does not work, remove the sending unit from the tank. Be prepared to buy or fabricate a new gasket, as it’s usually stuck to the tank. First, shake the float to see if it has been leaking. If there is any gas in it, it’s shot and will need to be replaced. We’ll test the sending unit to see if we replace the whole unit or just the float. To test, use a multimeter and set it to the lowest ohms scale (mine was 0-200). Place the positive (red) lead on the terminal that goes to the gauge and the negative (black) lead on the sending unit body making sure you have good contact (sand/scrape if you have to. Now move the float. At empty (float all the way down) it should read 0 Ohms (or close to it). At full (float all the way up, it should read 30 Ohms (or again close to it). If the unit works, you can buy a new plastic float from eBay. Look for one that fits a Jeep, 1955-1983 CJ5, 1955-1975 CJ6, 1976-1986 CJ7, 1981-1986 CJ8
3. Test for 12 volt supply on the gauge (the one from the ignition switch) if you find no voltage, fix/replace the supply wire.
4. Do a continuity test on the sending unit wire to the gauge. If you have an open fix/run a new wire.
5. Run a jumper wire from a known good ground to the back of the gauge cluster to insure the cluster has a good ground to the dash. If you gauge works you’ll need to clean up the area where the cluster touches the dash.
6. Unfortunately the next step is to remove the gauge (Disconnect your negative battery terminal before you start).This requires you to remove (or drop) the gauge cluster which houses the fuel gauge. I was able to lower mine sufficiently in order to remove the gauge. The bezel is crimped in a few spots which holds the assembly together. Using a small screwdriver, carefully pry open the crimps. Once the bezel, glass and inner trim are removed the gauge is visible. To remove the gauge, the adjacent gauges need need be loosened. There are two tabs (visible in the picture) that are behind the adjacent gauges and will prevent you from removing the gauge. Once loosened, you can remove the gas gauge. There are a few things to check. At this point, use the battery (or an external battery such as a motorcycle, tractor, auto, etc) so we eliminate any bad ground issues.
6.1. First let’s check if the gauge functions properly. Connect a jumper from the negative side of the battery to the sending unit terminal (the one with the red warning label). Connect a second jumper from the negative side of the battery to the gauge ground (shown in the picture). Connect a jumper from the positive side of the battery to the power supply terminal. Your gauge should go to empty. If it does not, the gauge is bad.
6.2. If your gauge checks out good, look at the back of the gauge where the gauge ground makes contact with the gauge cluster frame and clean/sand the contact area, insure there is no paint, rust or anything else inhibiting a good ground contact. Reinstall the gauge back into the cluster frame and tighten the nuts. Re-perform the gauge test but use the gauge cluster frame as the gauge ground. If the gauge now test good it’s time to reassemble. Tighten the adjacent gauges to the cluster frame.
6.3. There’s one more thing we need to check before we reassemble. Some of the reproduction gauges are made slightly thicker and the needle gets caught on the inner trim piece inhibiting the needles movement, making the gauge look like it’s not functioning. If you find this condition, a gentle push with your fingers will give you the additional clearance you need to keep it from binding. Mind you I do mean gentle as it moves easily and you don’t want to distort the inner trim piece. Once you have determined the needle moves freely, reassemble the rest of the cluster. The first time I installed the bezel, I used a screwdriver and a small hammer to crimp the bezel to the cluster and I felt it jared the cluster too much. The second time (yes, it took two times to get it right) I was able to use a needle nose pliers to get the crimps in. Protect the chrome from getting marred. Maybe some other “Bolters” have some other ideas on how to crimp the bezel on to the cluster. Now reinstall the cluster and hopefully it works! (Don’t forget to reconnect the negative battery cable)
7. At this point, we have eliminated everything but the sending unit. If your gauge still does not work, remove the sending unit from the tank. Be prepared to buy or fabricate a new gasket (you can’t use Silicone Gasket Maker as the gas will soften it and it will fail), as it’s usually stuck to the tank. First, shake the float to see if it has been leaking. If there is any gas in it, it’s shot and will need to be replaced. We’ll test the sending unit to see if we replace the whole unit or just the float. To test, use a multimeter and set it to the lowest ohms scale (mine was 0-200). Place either lead on the terminal that goes to the gauge and the other lead on the sending unit body. Now move the float. At empty (float all the way down) it should read 0 Ohms (or close to it). At full (float all the way up, it should read 30 Ohms (or again close to it). If the unit works, you can buy a new plastic float from eBay. Look for one that fits a Jeep, 1955-1983 CJ5, 1955-1975 CJ6, 1976-1986 CJ7, 1981-1986 CJ8.
Hopefully, at this point, you issue is solved!
Last edited by Phak1; 09/26/2022 1:36 PM.
