Hey guys,I had the usual problem with the fuel/temp gauge pegging to the right. I replaced the regulator with a newer one that has the IC internals. Now the temp doesnt move and the fuel barely moves. The gauges would also peg when I turned on the lights & go back when I used the left turn signal. That has also stopped. I let the car run for about 1/2 hour & no temp reading. Helllllllpppppp

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'72 Duster 198 stock cam, 3:23's Hookers on jack stands for 8 years in the driveway
'79 Maxivan 360 Offy Qjet Comp RV cam/rusting in the driveway.
93 D350 160HP Cummins Auto Dually Clubcab needs a injector pump
2005 Golden Couch Buick

If you don't have the back of the cluster grounded at all, the IVR will be confused. When you turn on the lights, you may be providing a small voltage difference (due to the voltage drop of the lighting load) that causes the IVR to turn on 100% which pegs the gauges.

I'm pretty sure that the IVR and the dash lights share the same ground - do your dash lights work normally, or are they rather dim? If you unplug your fuel sender and temp sender, do your dash lights stop working entirely? If so, you've found your problem.

All the dash lights seem to be working properly. I ran a seperate ground from the back of the cluster just in case.

Since your dash ground is good, see that the regulator is getting power OK and check it's output. The easiest way is to disconnect the temp sender and use a multimeter to look at the voltage (it ought to be around 5V) and then put on a 10ohm load and see if the gauge reads H.

(I forgot to ask the year, but if you have the IVR internal to the fuel gauge did you remember to disable it?)

If you've got the round multi-pin connector on your dash, beware that those pins can work loose and make intermittent or poor connections too.