Topic: Troubleshooting '67 Fuel Gauge

[drummingrocks]

I'm trying to track down a fuel gauge problem on my '67 coupe.  Since I've had bad luck with aftermarket sending units in the past, I assumed when the gauge stopped reading that the sender had died.  I replaced the sending unit with a Ford original, and the fuel gauge still stays at empty.  I had the car out over the weekend, and I noticed that both the fuel gauge and the temperature gauge were not reading.  That made me think it might be the instrument voltage regulator...but then I noticed that the oil pressure and amp gauges still read correctly.  If that regulator on the back of the cluster is bad, wouldn't it kill all of the gauges?  The dash lights, oil pressure gauge, and ammeter gauges all work, so does that rule out the instrument voltage regulator?

[midlife]

Only the fuel, oil pressure, and water temperature gauges work off of the constant voltage regulator.  The dash lamps and ammeter are on completely separate circuits.  Only the dash lamps on the dash need a ground.

If two of the three gauges don't work, I'd suspect a wiring issue, either on the back of the dash or on the sending unit lines going out to the units.  You can test the wiring by having the key in ACC, and removing the connector at the sending unit and briefly grounding it.  If the wiring is intact, the gauge should peg.

[ruppstang]

The first thing I try is grounding the sender wire. Doing that should peg the gage and tell you whether it is the sender or gage. If it dose not peg the gage you could possibly have a wire off or loose on the back of the cluster or a VR problem.

[drummingrocks]

Thanks, guys.  Can't wait to dig into it and see what's going on.  I'll update once I know more.

[drummingrocks]

Update:

I finally had a chance to look at it this past weekend.  I found a Mustang Monthly article from 2010 that detailed testing the gauges, and one helpful thing it mentioned is that there's no need to tear into the dash to test the IVR.  I pulled the lead of the temp sender and hooked a multimeter to it.  When I saw that it wasn't pulsing with the key on, then I went ahead and pulled the cluster.  Before I even had it all of the way out (the original dash pad on my car has swelled and distorted so that it's really hard to get the cluster in and out), I could see the problem.  The connector that connects the cluster wiring with the main harness had come partially unplugged.  I have no idea how any of it was working at all; probably about 3 pins were making contact between the cluster connector and the main wiring harness connector.  Apparently that was enough for the dash lights and, for a while, the temperature gauge to work--what are the odds of that?!     Anyway, I put the connector back together, and all is well.  Thanks for all of the help and advice!