My fuel gauge goes slowly over to past full when the ignition is turned on and tank is nearly empty. (I should also say that the TEMP light doesn't come on like I think it should when the key is in START position. Might be a clue. Haven't pursued that one yet.) With key in run position, there's no voltage at either of the wires at the sending unit. Pulled the instrument cluster and there's no voltage (key in run position) at either terminal on the fuel gauge. There's a part (C9AF-18A952-A) with 9V battery style connectors mounted on the back of the instrument cluster (lower left of first picture) that I'm guessing limits the current thru the gauge. I get voltage to one side of that part but nothing on the other side. My ohm meter shows an open condition across the terminals. So, I'm guessing its bad and I need to find another. Anyone have another idea of what's wrong? Probably can't buy a new part, right? Anyone have one that's good? Thanks for any help. Hope there aren't too many more of these mysteries.
Didn't see your second post till after I ordered one off ebay. Getting this one http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=270584109610&viewitem= The one you suggested, and a few others I saw, have the terminal positions reversed as compared to mine. Didn't know if I could just flip it around and snap it in or if that would reverse the input and output???? The more I learn the less I seem to know. Did find one that looked correct at a Mustang supply (don't recall which one) but it was almost $70. Thanks very much for your help. :Handshake I was stuck. Hope it fixes the problem.
Wire Shorted I was poking doing some more testing on the fuel gauge circuit this afternoon. Unplugged the terminal at the tank so I could put voltage on the instrument cluster end of the wire and test for it at the tank connector -- testing continuity. But when I put the hot wire on the instrument cluster end I got a tiny spark -- with other end of the wire disconnected. Ah ha!! A short!! Pulled the connecter apart at the rear quarter -- no spark at the cluster end. Short must be between the rear quarter and the tank connector. Removed that piece of the harness and discovered someone had replaced a section of the hot wire. Soldered the joints and put heat shrink on it. But, he must have overdone the heat 'cause the wire insulation inside the heat shrink had been melted. Saw a few places where there could have been slight contact between the hot wire and the ground wire. Redid that section of the harness and now the fuel gauge reads just above empty. Can't be more than 2-3 gallons in the tank. But, the voltage reading on the output side of the instrument voltage regulator is jumping around (think that part's normal) and showing only 10ths of a volt. Will be interesting to see what happens when I put some gas in it. May not need the new regulator. (Glad I didn't go for the $70 one!) Maybe I was getting zero voltage on the output side of the regulator 'cause the wire was shorted out. Again, thanks for the help.
It's interesting, too, to find out how accurrate the gauge really is. At one time I added a ground wire to the sending unit plate because I wasn't getting a good ground through the tank anymore. I drained the tank and took out the sending unit, added a ground connection and reinstalled. Putting gas back in the tank on level ground I found that even after dumping in 2 gallons the gauge still read empty. Another half gallon and the gauge started to move.
If your volt meter reading is jumping around...The IVR (instrument voltage regulator) is working. Once you fix your short you should be good to go as long as the fuel level sender is good. Often times the float will get a pin hole in it,filling with fuel and sinking.(My Sprint did this to me) While you have a small amount of fuel in the tank,I would pitch the driverside of the car up at an angle and pull the fuel sender out of the tank. With the wireing repaired and the sender hooked up,move the sending unit arm up and down to be certain the system is working. Make sure the float doesnt have fuel sloshing around in it too. Good luck!!!
I have a new Mustang tank and new sender/pickup. Should be good to go. Actually, I prefer it to show empty with a couple of gallons left. Just a little cushion for those times when you stretch it a bit. And, its not going to pull the last bit out anyway. New tank has a drain plug if I need it.
