Posted by Sherman in Idaho [108.162.246.24] on Wednesday, August 31, 2016 at 16:02:23 :
In Reply to: Re: 6v-12v Gauge Problem posted by Greg Coffin [172.68.35.21] on Wednesday, August 31, 2016 at 15:52:52 :
Remember, the gauge needs three connections -- power in, wire to the sender, and a ground. Not sure exactly which kind you have but they generally use a balanced coil arrangement in which the hot lead goes to two coils, one of which has its opposite end connected to ground directly via the gauge case and mounting bracket, and the other of which goes to ground via the sender. One coil pulls the pointer one way and the other one pulls it the other way. The advantage of this scheme is that it compensates for variations in battery voltage so the pointer doesn't go up and down as you rev up the engine. The problem is that with 3 connections, one of which is "hidden", it can be confusing to get it wired up correctly. To make it worse, various mis-connections will still result in the pointer moving (usually pegging).
So, first of all make sure the sender AND the gauge housing are both grounded to each other and to the correct battery terminal (positive or negative doesn't matter). If it's still not right, try swapping the "hot" and "sender" leads at the 2 screw terminals on the back of the gauge. Or use an ohm-meter to measure the resistance to ground (case) from each screw. The "hot" terminal will have the lowest resistance because the current is only going through one coil, while the resistance will be higher (not twice as high, but in that range) when you measure from the "sender" terminal to ground, since the current is going through both coils then.
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