Fuel Gauge Question

79X19

79X19

True Classic
Just finished installing my reconditioned dash after many months of preparation and work. Now I believe that the fuel gauge is not operating. I'm pretty sure that I have a half tank of fuel and when i move the key to the on position just before engaging the starter shouldn't the fuel gauge jump to life and show that I have a half tank of fuel? My volt meter is working and the various dummy lights are illuminating but no fuel indication. I am going to check my fuse box for loose fuses and maybe blown fuses but anything else that I should check?
 
I can't comment about the exact source of the problem, but I can confirm that the expected behavior you describe is correct. As soon as the ignition switch is in accessory mode the fuel gauge comes to life and shows the fuel level in the tank.
 
Actually, I can comment about the source of the problem, but I'm not sure how useful my comments will be. It's almost certain to be a loose connection -- the question is where? It's likely to be close to the part worked on -- the dash. I believe the fuel gauge uses small bolts to help transfer voltage from the circuit board to the meter movement. I would check that those are nice and tight first. If those are already tight, then someone smarter than me might be able to tell us what voltage range is expected at the fuel gauge terminals, from empty to full, so that you could use a multimeter to trace the missing voltage backward towards the tank.
 
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Thanks for the info. I thought that was the case but I haven’t had the dash back in the car In 18 months so my memory is bad. I’ve attched a photo of my dash all assembled and the thought of digging back into really is a bummer. I just spent god knows how many hours fixing tons of things to get it to this point and now this. UGh!!! Oh well been thinking also when I was changing out he speedo cable I could have disrupted the wires for the sender at the fuel tank. Don’t know for sure but electrical gremlins are a time killer!! Thanks again for the info.
 

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The needle could also be mechanically stuck.
You could hit the top of your dash with a flat hand just to see if it does something.
 
Your dash looks great. Also check to see if the sending unit is working. They can be finicky, especially after sitting. Use a multimeter to check for resistance while moving the float arm up and down. The resistance level will have a low and high reading at each end of its travel (don't recall what those are at the moment but I'm sure they are in the factory workshop manual - available on the forum). But more importantly, does the resistance value change with any movement (with a stuck float it will not change). With some fuel in the tank, you might be able to just shake the car enough to get some sloshing and check it as the arm moves. Otherwise remove the sending unit to test it better - easy to do.
 
79X19 said:
I’ve attched a photo of my dash all assembled and the thought of digging back into really is a bummer.
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Looks nice! Have you done an LED lighting conversion for the instrument panel? The reason I ask is I've done that for both of my X1/9s and the work was fussy enough that I got really comfortable moving the instrument panel in and out, and in and out, before those upgrades were complete. Indeed, I'm planning to remove both instrument panels again to add small resistors to the turn-signal LED and the headlight/running light LED, so they are not so bright at night. My current plan is to have a relay that keeps the turn-signal LED bright during the day, when it's competing with the sun, but dims it during the night when it's way too bright as-is.
 
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My '82 X already had the dimmer controlling the main instrument panel lights, without any change on my part (it's also from a model-year when the instrument panel illumination is on all the time, day or night, as long as the car is on). The dimmer is the modern electronic style and works perfectly with my LEDs. Don't want to add the turn-signal LED to that, because I want its illumination to be correct for itself day and night, without upsetting the setting that works well for the rest of my dashboard illumination. The warning LEDs will also not get any resistors, because they should be as bright as possible, day or night, to catch my eye.

I might use a variable resistor with the turn-signal LED so that it's not fixed but could be tweaked until the night-time setting is to my liking.

The '85 X is a different story, with some of it better (dashboard illumination on only when the running lights/headlights are on), and some of it worse (the dimmer does not dim the 4 main instrument panel lamps). I'm hoping to rewire both cars so that they each have the best of both model year wiring decisions. Ultimately, both cars will only have the dashboard lights on during the night, but they will be a part of the dimmable circuit.
 
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Thanks all. The dash is from my 79 parts car and needed reconditioning to get it to this point. It was brown and I had to mod one of the support arms from the 81 dash to fit it in the 81. Also had to dremmel out the cig lighter hole to fit the 81 cig lighter. Painted it with SEM vinyl dye, re did the glove box hinge then recon the heater box then the pedal box all the hoses, masters, then the accelerator cable, speedo cable, heater hoses, brown wire mod, front speaker wires, windshield surround replacement......all leading up to being able to reinstalling the dash. And now the gas gauge says F-U!!! LOL!!! These cars will drive you to drink and if they weren’t so fun while getting you there why would we do what we do!!!
 
Just connected the wiper motor back into the system to see what that would do because its on the same circuit according to the wiring Manual. Well when in put the key to the on position and turn the wiper motor on the the intermittent setting the brake oil and fasten seatbelt lights and the fuel gauge comes alive both lights and gauge flicker only when the wiper motor comes on and off. The gauge goes on and off to the cycleing of the wiper motor. When I turn the wiper Motor the medium and high settings the lights and the gauge go dead. I’m thinking because I don’t have everything hooked up yet that circuits and grounds aren’t complete and somehow this electrical Cirque du soleil I am witnessing is the by product. Could that be the case?
 
79X19 said:
I’m thinking because I don’t have everything hooked up yet that circuits and grounds aren’t complete and somehow this electrical Cirque du soleil I am witnessing is the by product. Could that be the case?
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I like the term "electrical Cirque du soleil"! Makes me imagine gremlins doing their acrobatic feats of daring splendor!
. . . . :D
:D__:D/
. \:D/
. . :D

I think your conclusion is solid. Until the grounds and wires are all where they're supposed to be, I would recommend assuming things will not work properly. I wouldn't waste any more time troubleshooting the fuel gauge behavior unless you're still trying to figure out where the grounds are, and where the wires are supposed to go.
 
Make sure the ground wire lug is connected under one of the sender unit nuts and that the connection is metal to metal and clean. If that one is open, the low fuel light won't work right either.
 
So I went through the grounds. Check. Checked connection at the sending unit. Check Went ahead and took the gauge cluster back out and cleaned the connectors made sure nothing was out of the ordinary then reconnected.
Tested by turning the key and what do you know the fuel gauge came to life. Shows a half a tank of i'm sure old gas but the good news is that its functioning!!

Turns out that is must have been a dirty connection from the wire harness to the gauge cluster.
 
I had mine working beautifully until I had to remove the instrument cluster again. Now it works but I have to give it a thump with my finger every time I turn the ignition on. Temperamental little things, aren't they?
 
Yes they are. Mine just quit working again. I took out my 79 cluster and put the 81 back in to test to see if the gauge was bad, It doesn't work either. Maddening Cant progress with other work till this is taken care of
 
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