Fuel gauge doesn't work
Discussion
You should have a + on one side of the gauge from the voltage stabiliser (I think it regulates the voltage to around 11/12Volt, check this as I am not 100% sure) and also a negative from the fuel tank sender unit and that can be shorted to earth to check for full swing of the gauge needle
If you have both + and - at the gauge yet it doesnt work, the gauge is faulty
If you have both + and - at the gauge yet it doesnt work, the gauge is faulty
I'd suspect the wiring first and the sender second. The wiring to the sender is pretty exposed in the wheel arch, and the sender uses a crude mechanical potentiometer which can wear out.
If the sender and its connections look sound consider whether the alarm may be interfering. I don't know how widespread it is, but I've seen alarm installations where the immobiliser intercepts the circuit to the fuel gauge as well as disabling the ignition.
If the sender and its connections look sound consider whether the alarm may be interfering. I don't know how widespread it is, but I've seen alarm installations where the immobiliser intercepts the circuit to the fuel gauge as well as disabling the ignition.
If touching the wires together as per Phillpot above makes the gauge work then it could possibly be the sender. At the Practical Classics show the other week I saw an 'S' gauge labeled "MG Midget post 1972". Only £20 from memory so maybe check out that alternative. This is assuming you have the two wire/three terminal type like this...
Totally agree that the first thing to do is check wiring at the sender. Jack up and remove left rear wheel (can be done with wheel on but difficult to be sure so take the wheel off and get it right!). Sender is in the side of the fuel tank. First clean both connectors carefully and ensure there is good contact with the sender terminals, test to see if the gauge starts. If it does then waxoyl and protect the connectors.
If not, disconnect the coloured wire (should be green with a black tracer but may have been changed) and earth it to the black wire. If the fuel gauge works then the sender is suspect. But you cannot yet rule out a wiring problem.
Connect a bit of wire to the coloured connector and earth this direct to chassis (a clean point like the fuel pump mounting bolt). If the gauge works the problem is the earth wire from chassis to sender. That wire is very vulnerable and connects to a stud on the top left of the chassis. Clean up, used serrated washers for electricalk contact and waxoyl over.
If none of that works then next check wire from sender to gauge using a continuity tester, that wire goes in to the boot and into the main loom.
If you have to replace the sender please check on further advice on PH posts. It is easy to get a sender to fit the housing on the tank (Car Builder Solutions do one but other items will fit), the issue is to get the arm inside the tank right! Most are too long and there is a baffle in the tank that they hit, or the angle of the arm needs to be changed or the reading will only work through part of the range. I did put dimensions on a post.
If not, disconnect the coloured wire (should be green with a black tracer but may have been changed) and earth it to the black wire. If the fuel gauge works then the sender is suspect. But you cannot yet rule out a wiring problem.
Connect a bit of wire to the coloured connector and earth this direct to chassis (a clean point like the fuel pump mounting bolt). If the gauge works the problem is the earth wire from chassis to sender. That wire is very vulnerable and connects to a stud on the top left of the chassis. Clean up, used serrated washers for electricalk contact and waxoyl over.
If none of that works then next check wire from sender to gauge using a continuity tester, that wire goes in to the boot and into the main loom.
If you have to replace the sender please check on further advice on PH posts. It is easy to get a sender to fit the housing on the tank (Car Builder Solutions do one but other items will fit), the issue is to get the arm inside the tank right! Most are too long and there is a baffle in the tank that they hit, or the angle of the arm needs to be changed or the reading will only work through part of the range. I did put dimensions on a post.
greymrj said:
...... Most are too long and there is a baffle in the tank that they hit, or the angle of the arm needs to be changed or the reading will only work through part of the range.....
If you can use the Land Rover/Midget part you can swap the arms over simply by unclipping them.
Showing full implies the gauge output to the sender is being grounded. Disconnect at the sender and see whether the gauge shows empty. If it does, the problem is in the sender; if it doesn't, the wire is shorted to ground or you have a faulty gauge. If you have somebody with enough elbows you could disconnect it at the gauge to find which is the case.
I was looking for one a few weeks ago for my S1, not tested my old one yet or bought a new one, here’s an picture of the old one and the closest I could find that looked the same, though the tube is longer than my original. Hopefully of some help.
Edited by 88S1 on Wednesday 1st September 22:00
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