Electrical Gauge cluster woes...


Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
Hey guys,

I'm asking for a little insight into a problem we are having with Scarlet...1986 5.0 Lx all stock.

Yesterday during a drive the temp and fuel gauge bottomed out. When turning the key to run without the engine started they both read high. The actual engine temp was about 190°. When the car is started they both drop to cold and E. We went through the EVTM and found the fuel and temp have separate grounds...obviously because the temp grounds at the engine and sending unit by the hatch latch. The only common side is the wire from the ignition switch through the cluster voltage regulator.

The issue is the cluster gauges only have power in run and accessory. Key turned on is run...whether the actual car is running or not. That circuit shouldn't change. The alternator is putting out 13v with headlights and fog lights on.

Has anyone here seen this issue and fixed it ?

We are ordering a new cluster voltage regulator regardless. I haven't checked voltage at the cluster connector or ignition switch yet. Should be a black w/ light green wire.

Usually, a bad voltage regulator will cause gauges to flicker or not work at all. I guess in some weird way it could heat up and fail when the car is started due to the alternator putting out more voltage.

The Ol' Lady really wants to drive it and my time might be a little limited until the end of November.
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I would start with the voltage regulator and go from there. My Saleen gauges started going all over the place a few years back. Replacing the voltage regulator solved that problem for me.
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Consider the ignition switch (I keep a known-good one around for diagnostics) and retrace the wiring to ensure there's not a ground short.

I have a spare column with a known good ignition switch for her. I'll check into it.