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Electrical Gauge cluster woes...

  • Thread starter Thread starter 90sickfox
  • Start date Start date Oct 6, 2022

90sickfox

Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
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Oct 6, 2022
#1
  • Oct 6, 2022
  • #1
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.
 

TIGGER

Founding Member
Mar 6, 2000
877
244
104
Portland, OR
Oct 7, 2022
#2
  • Oct 7, 2022
  • #2
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.
 
Reactions: 90sickfox

FastDriver

I was uncomfortably high & wearing a helmet
SN Certified Technician
Sep 5, 2001
6,104
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Vass, NC
Oct 7, 2022
#3
  • Oct 7, 2022
  • #3
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.
 
Reactions: 90sickfox and Noobz347

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor
Admin Dude
Jan 4, 1985
43,145
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Box behind Walmart
Oct 7, 2022
#4
  • Oct 7, 2022
  • #4
FastDriver said:
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.
Click to expand...
bingo
 

90sickfox

Wasn't a pretty sight...and I've got big hands
SN Certified Technician
Mar 2, 2015
6,945
5,816
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Oct 8, 2022
#5
  • Oct 8, 2022
  • #5
FastDriver said:
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.
Click to expand...

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