Instrument Panel Ground?

[gusexcel]

1987 Excel SE
Anyone know the physical location of the instrument panel ground?

I had mentioned previously that my instruments varied when the fans switch on, or the headlights are on.

I just checked the voltage at fuse 13 and it does not dip appreciably[about .1 volt] when the fans switch on,referenced to engine ground. Unless there is a bad connection between the fuse and the instruments, it must be grounding.

The indicated temp will rise at least 2 degrees when the fans kick on. 2 or 3 more when the headlights are on.

The car is running a bit hot with the AC on, but that needs to be determined.

[Pete Boole]

There is a grounding stud (M8) above the relays on the pedal box - I would think that's where the panel earth would be.

Pete

[gusexcel]

Pulled the dash out enough to put a jumper from the volt gauge to the engine block and it helps a little, the temp gauge does not dance as badly with the blinkers

I have checked the voltage at the alternator and battery and it reads 13.7-13.8 depending on load at idle. The volt gauge reads 12.5 or lower with headlights on or other things running
The instrument fuse likewise
Interestingly the instrument harness appears to have been spliced, neatly, and each wire covered with red heatshrink. It could have been damaged at some point. Since it appears that since every individual gauge power feed and ground goes back into the harness that I still need to find the source, unless I want to rewire the back of the dash.
One interesting thing is that the drivers door post[LHD] is not grounded, while the passenger is.

I suppose if I detach the speedometer I can get the dash out completely, and wire a new power and ground harness on the back of the dash, but I am not sure that it will do the trick

[Pete Boole]

The original harness has several splices as well - some of them ground returns IIRC. Might be worth trying to find those behind the dash panel and check their integrity.

Pete

[gusexcel]

OK, so while I wish I had a better understanding of the problem, it appears it is fixed

I bought these
https://www.mcmaster.com/72065K22/
or these would be good
https://www.mcmaster.com/72065K151/

and built a daisy chain for power and ground for the volt gauge, temp gauge and oil pressure gauge[don't care about the fuel, ok]

While the volt gauge has just two discreet terminals, the oil and temp gauges have a housing similar to a headlight connector with 3 terminals in a plastic housing. Pushing a piece of 16 gauge[solid] wire into a notch the housing will allow you to push the terminal end out.
So all OEM wiring remains in place, but there is now a 12 volt and ground 'buss' for the gauges. The power goes to a 'scotchlock' terminal

https://www.mcmaster.com/69515K24/

on the green wire coming from fuse 13[top right fuse in the fuse box near the steering wheel] The ground wire I fished over to the radio ground. Since I was adding a new radio to comply with hands free laws here, I also fished a ground wire along with the USB and AUX wires over to the passenger side footwell. If I feel the need to find a good solid ground beyond what is there I do not have to take anything apart

while it is not as hot as it has been, low 80's F, the indicated temp is much lower. Idling for a long period and putting around town engine temp did not exceed low 90's C
The temp rose to 98 or so when I blasted onto the highway, but quickly came down to low 90's at cruising speed, and did not rise again when putting down the mile of side roads to my house

It is my feeling that the effect of voltage drop in the system is a bit non linear, and starts exaggerating is the gauge departs center scale.

Headlight, fan, AC clutch. radiator fans, I still see some movement, but previously I was seeing at least 5 deg C total and now I am seeing maybe 1 degree, I think.

On a very hot day a few weeks ago I was seeing indicated temps as high 105C, which I knew was wrong, but I was unsure how wrong.

I feel more confident now