Re: B1 Fuel gauge


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Posted by David Sherman [72.47.9.228] on Thursday, January 13, 2011 at 22:56:06 :

In Reply to: B1 Fuel gauge posted by David N. Lundstrom [64.68.11.101] on Thursday, January 13, 2011 at 21:52:00 :

I don't know about that gauge in particular but generally one is hot (to the ignition) one is ground (often connected to mounting bracket, which is sometimes a pretty poor ground), and one goes to the sender. Sometimes the grounded one is grounded inside the case of the gauge and you need to make sure the case is well grounded. Basically there are two coils inside the gauge. One pulls the pointer one way and the other pulls it the other. This helps compensate for variations in battery voltage since if the battery voltage goes up, the current through the sender's coil goes up, but so does the current though the grounded coil.

If you have no markings and no known gauge to compare to, one way to figure out which is which is measure between each pair of terminals (three measurement) with an ohm meter. When you find the pair that has the highest resistance, the other one is the hot terminal. That's because in that position, you're measuring the resistance of the two coils in series. Now hook that wire to a 6V source and try momentarily grounding each of the other two. One should make the needle bang against the "empty" stop and the other against the "full" stop. Assuming the sender has minimum resistance when the tank is full, the terminal that made the pointer hit "full" is the one that goes to the sender. It really helps to test his on the bench using a spare sender and a few clip leads. Hopefully you can find a wiring diagram that shows your gauge with its 3 terminals and you won't have to figure it out the way I just described. It's still a good idea to bench test it so you don't end up going around in circles in the "is it the gauge?", "is it the sender?", "is it the wiring?" loop.



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