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This is an electric gauge, right? (I don't think you said which car.) May be different on some, but on Saabs I know about, the system is pretty simple. Gauge gets 12v supplied to it on one terminal, other terminal runs via wire to the sender, which is screwed into the block. Sender is a resistor, the resistance of which varies with temperature: low temperature = high resistance and vice-versa. When the engine is cold, the sender allows very little of the 12v to leak through to the block, so the gauge reads low. As the sender gets warmer, it allows more and more of the 12v through so the gauge reads higher.
Knowing this, you can check it out. Pull the wire connector off the sending unit and ground it to the block. Now there's no resistance to ground, so needle should go all the way up (with key on, of course.) If it doesn't, you have bad wire, bad gauge, bad ground, etc. If it does, problem is in the sending unit; you'll need to replace it.
-- If the sending unit is OK, then you need to get to the back of the gauge. Pull off wire that comes from sender, ground the terminal to which it connected. If the needle goes up, you've isolated the fault to the sender wire. If the needle doesn't move, then either you've got a bad gauge or it's not getting 12v on the other connector; check with a voltmeter or test light.
-- If it seems to be the wire: just to make sure, before you go through all the headaches of tracing along the wire, make up a long jumper wire with the right connectors on both ends; run it from gauge, out the window, down to the sender and hook it up to that. Now see if the gauge works correctly. If it does, you know your problem is in the sender wire or the connectors along that wire, and you just have to work your way along it until you find the problem spot. I'd suggest starting at the engine end because that seems to be where it's more likely to go bad (because of all the heat, vibration, etc.)
posted by 68.13.13...
, Mon, 21 Apr 2003 13:19:11
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