Instrument Cluster Illumination became erratic then died

NJ95-850GLT · Post by **NJ95-850GLT** » 11 Mar 2011, 18:49

1995 850GLT began erratic illumination of the instrument cluster, sometimes the lights were on but would occasionally blink on & off, now they went off completely. All of the gauges work and warning lights illuminate, but I can't see any of them including the speedometer at night. I pulled the dimmer to check for corrosion on the pins or in the molex plug, all clean. Any tips to bypass the dimmer and test the cluster without pulling the dashpad would be appreciated. Bob

NJ95-850GLT · Post by **NJ95-850GLT** » 11 Mar 2011, 19:34

PART 2: I just pulled the schematic from the wiring diagram section of the Repair Database, I'm looking to see if I can bypass the reostat/dimmer portion to see if the lights are restored. At 204K... electrical gremlins can be anywhere and I don't want create a short or bigger problem.

Post by **precopster** » 11 Mar 2011, 19:55

Probably the easiest repair I've ever done!!

Lever out the fog lamp switch beneath the dimmer, then lever out the dimmer, pull off the connector, slide on a used dimmer from a wrecker then re-assemble in reverse order.

After pulling apart the old switch to see if there's anything obvious you wouldn't believe how complex the circuit board is for such a simple function!! I couldn't see any dry joints, so I assume a component went out of tolerance.

The slide lever doesn't alter the resistance relationship b/w other terminals when it is sliding when the unit is not powered up.
One of the other posters on the forum said he circumvented it by shorting pin 1-4 of the connector (there are six of them)

NJ95-850GLT · Post by **NJ95-850GLT** » 11 Mar 2011, 20:22

Thanks Mate... I was leaning toward this route since the slider didn't feel as there was any resistance when moving. I was hoping to jump across the reostat to prove the failure before spending $$$ on a guess.

Post by **precopster** » 11 Mar 2011, 20:33

It's a 20K resistance down to a short on full deflection of the slide lever. Give your slider a test (out of circuit) before getting another.

NJ95-850GLT · Post by **NJ95-850GLT** » 11 Mar 2011, 20:46

and that's on pins 1 & 4 of the control when pulled? I think you're on to it... The slider on the control just feels whimpy as if theres no contact on the potentiometer.

Post by **BEJinFbk** » 11 Mar 2011, 21:04

That thing is really a little variable power supply.
The slider is just the human interface for the transistor in there.
That's why you won't see it vary anything at the pins.

NJ95-850GLT · Post by **NJ95-850GLT** » 11 Mar 2011, 21:34

I'll keep you all posted.... Snow is gone, the Flood waters are receding, and my tools won't stick to my hands anymore. Not to mention that we all have an extra hour of daylight this weekend (USA). My referance as to the feel of the slider, is that there is hardly any feeling of contact to anything in order to regulate a power variance. Granted solid state controls offer little physical contact, but there has to be a readible circuit of variable resistance with a common Ohm Meter.

Post by **precopster** » 11 Mar 2011, 23:18

It's 20K ohms across the two left most (centre and left) of the three terminals on the slider. When in full deflection in the other direction it gradually goes to almost zero ohms.

Pins 1 to 4 on connector were about 9K and don't vary with slider function (at least not when it's unpowered).

Pretty much from the other posts I've seen it's usually (about 90%) the dimmer switch.

Some people have reported the ignition switch to be the culprit.