so, the gas gauge on a buddies fj40 does not work. as I understand it, there are only 3 reasons why (let me know if there are more). 1. bad wiring = loose, cut, old 2. bad gas gauge at the dash 3. bad relay switch so, without spending a bunch of money and wasted time, how do you best determine what the issue is, then get the part/fix you need?
In stock configuration, there is no relay in the circuit for the fuel sender gauge. When you check the wiring, make sure you have good ground.
Remove the sending unit and make sure that it has the proper ohms resistance. Remove the signal wire from the top of the sender, and ohm it back to the gauge, and make sure there is not an open in it. Make sure that your ground wire, that attaches to one of the sending unit mounting screws, is actually a ground by putting the ohm meter between that mounting screw, and a known good ground (frame?). If both these all check out, then you would certainly think that the instrument is to blame. In my experience with this issue, the things listed above have all been found at fault. Good luck! -Steve
poser - would any of this be changed if there was a 2nd tank added. there is a front and a rear tank setup. if the gauge does not work, we at least want the gauge to register the orginal tank as it should, could that 2nd tank be an issue or cause. or, are we still at your suggestions Poser?
Relay controls power to a component. Sender transmits information back to an instrument or display. If for some reason, the original wire has been hacked into, trying to get the second sender to work on the single gauge, I would look at the wiring there first. You will find a multimeter a very valuable tool for figuring out this issue... Good luck! -Steve
Regarding a second tank, you can have both tank sender units wired through a simple switch to determine which sender the guage will read. Obviouly, you will only read the tank selected. There are no relays involved. Make sure the tank is grounded - with a wire from the sender unit mounting plate to a reliable ground point on the chassis,... don't rely on the mounting brackets to complete your circuit.
I 3rd or 4th the ground on the sending unit. I usually reach under and fiddle with the wire and it gets the good ground. JJB
so, I get the impression that most of you think it is more likely a bad wiring issue (grounding of it) then it would be the actual expensive gauge itself.
