My car learned a new trick... - Third Generation F-Body Message Boards

rtchaney · 11-05-2009, 08:34 PM

Well, my '89 RS now has an intermittent gas gauge to go along with the tach that shows my idle a 3-4k and pegs at the shift points; FUN! I have only one working light that illuminates my excessive bouncy speedometer for the cherry on that cake... Should I just replace the cluster? Please note that the car runs flawlessly, well, for now. Oh, the voltmeter works! My Hanes manual tells me how to replace the cluster I just want to make sure that I shouldn't start with something more simple or cheap first. Thank you.
- R

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radical82 · 11-05-2009, 09:08 PM

It's been my experience that intermittent and erratic gauge problems are often a ground problem.... Might want to check the ground for your gauge panel and the ground for the fuel tank sender.....

rtchaney · 11-05-2009, 09:19 PM

Makes sense; not to be foolish, where are those located? I thought that the sending unit was grounded out to the fuel tank itself by the spinning locking hoober-doober that hold it in place. As for the cluster itself, I'm at a loss. Would it be in the dash or at the end of the harness?

radical82 · 11-05-2009, 09:42 PM

I'm certainly no expert on 2rd gen wiring, but generally the sending unit should have a ground wire that comes off the sender itself and grounds either to the frame in the rear by the tank, or in many instances the ground is in the same harness as the wire going to the gauge. As to the ground on the cluster, I'd have to research a schematic, but (again) generally there is a ground post on the printed circuit or wiring harness to the gauges that is grounded under the dash near the gauges themselves.... As a car ages, the wiring deteriorates, plus moisture and other contaminents can make their way into harnesses, and especially to where the ground wires are attached to the structure.... A quick look to locate the grounds, then some sanding paper or a small wire brush to clean the area where the wire is attached should cure a bad ground.... I also coat my grounds after they are cleaned with dielectric grease to slow down the process of moisture causing corrosion and recreating the problem....

A long answer I know, but it could well be a bad ground or grounds... Perhaps time for a bit of light maintenance on the wiring harness to redo all the ground points may well cure the present problem as well as preventing future problems....?????

NINÅ · 11-10-2009, 12:06 PM

However your tach problem is probably not as simple as a bad ground.

After you check your grounds and the tach does the same thing look at the circuit inside the dash that moves the pointer.

It’s contained on a small plug-in PCB or integrated in the main board.

On the PCB you’ll see a resistor chip.

Desolder pins 4 & 10.

Use a 500K potentiometer.

Solder it across traces 4 & 10.

Move the potentiometer to half way.

Start the engine and compare the tach reading with a test equipment quality tach.

Dial it in, unsolder one side of the potentiometer, measure it and buy the matching resistor.

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If People Drove Any Slower They’d Be Going Backwards

Fog lights are not driving lights. They look doofy. Turn em off slow pokes.

How bout those nervous nellies too scared to drive without headlights on in the daytime or if there is a little rain!

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