How to test a 0-95 ohm LED sender unit system is working.
If your unsure if the 0-95 ohm sender unit is working correctly there are a few simple procedures and tests ( which also checks the wiring at the same time )
Always do a visual check first to make sure the wiring, tank sender unit and LED is wired and powered up. If the tanks been installed for some time then always check the tank 0-95 ohm sender unit ( the clock face with the green and black wire coming out of it ) for water ingress as any water in the sender unit itself will give spurious readings as moisture will affect the senders resistance.
If the LED unit is not reading the correct gas level on a new tank ( even if you know its full but your seeing empty ) before removing any item please check to see what the tank sender unit ( the clock face with the green and black wire coming out of it ) is showing and make a note of the % the needle is showing on the clock face. This sender unit in the tank connects to the led display via 2 cables and the gas level sender in the tank picks up the gas level via a magnet inside the tank valve. If the magnets are not aligned then the led display in the tank will never show you the correct gas level.
The first test we always recommend would be to remove the 2 small screws holding the tank clock face in place ( DO NOT REMOVE THE 4 ALLEN BOLTS FROM THE TANK VALVE ) and put a magnet on the back of the clock face and move it round to full or half way. Then go an check if the LED is showing a higher gas level. If this works correctly then we would recommend leaving the clock face set to 50% and refit in the tank - This will display the wrong gas level until the gas level in the tank falls and the internal magnet passes the clock face magnets. After both magnet align then it will work in the future.
If the above doesn't work and you are unsure if the items or wiring are faulty please follow this below :
1) Disconnect your 2 wires going from your tank sender unit up to the 12 volt LED unit you have fitted inside the vehicle ( disconnect the 2 wires up at the LED display ). These 2 wires of yours will be connected to the green and black on the LED unit.
2) Set your voltmeter to read ohms.
3) Connect your meter probes to the 2 wires going from the tanks 0-95 ohm sender on these 2 wires ( the wires form the tank, not the LED display )
4) Remove the 0-95 ohm sender from the tank - it is held in the tank float valve by 2 small phillips screws. DO NOT REMOVE THE 4 ALLEN BOLTS as they hold the float valve in the tank which will be under pressure. ( see attached document )
5) Put a magnet on the rear of the 0-95 ohm sender unit and using the magnet move the hand on the front around from empty to full / or full to empty.
6) Check your meter and when going from full - which will read approximately 95 ohms around to empty - which will read approximately 0 ohms you will see various readings.
7) If there are no reading changes on your meter then the fault could be the sender unit itself or your 2 wires from the tank. Disconnect the black and green wires at the tanks sender and reconnect your meter directly to the 0-95 ohm tank sender unit and run the same tests as point 5 down again. If they read ok at the sender unit then the fault is your wiring going from the tank to the LED unit. If you get no movement in your ohms reading when wired directly at the 0-95 ohm sender, then your sender unit is faulty.
If you find water has got into the tanks 0-95 ohm sender unit try blowing the moisture out with air and re test. If water has been in there for some time there might be extensive corrosion which will deem the unit beyond repair.