MainePorsche

Just curious, how are the dash, pod, and console lights on when the light switch is off ? Did you mean the illumination cut out when the switch went from position 1 to 2 ? I still think it's a shorted light switch via the Black/Blues and not the rheostat. Typically if the rheostat is shorted or open you will never have illumination through it.

Hilton

He has an 89 - its nothing like your dash

Gregg, Ed's got it right just above.. twiddle the rheostat back and forth a bunch under the lip of the pod. Its likely just minor corrosion and a few turns each way should get you back to working dash lights.

Note that they're on FULL bright with the lights off, and that once the headlights are turned on, you won't be able to get them as bright as they are with the lights off.

You can bypass the rheostat if you want, but just turning it end-to-end a few times should restore function.

j.kenzie@sbcglobal.net

Hi Gregg,
Are the instruments lit when in parking lights position? Are they dark all the time or just when HL is on?
Dave

MainePorsche

My error.
Sorry Gregg.
Thanks Hilton.

Gregg K

It's the dimmer. It appears to ohm properly. But when I bypassed it, and connected the two dimmer wires together, I had dash lights. Now when it's connected, I get lights, but the dimming is erratic. So it's corroded. Time to massage it.

Thanks you guys! You're the greatest.

Alan

It is not likely to be the headlight switch - leave it alone for now.

This is essentially normal behaviour... yes I know it doesn't work ...

The pod is illuminated by a different circuit when the lights are off Vs when the lights are on.

The pod gets full brightness illumination in daylight when the lights are off. This is so if you enter a tunnel you can still see all the instruments - there is a photo sensor at the top of the dash face that further controls the brightness depending on ambient light in this mode...

When you turn the lights on - the pod illumination is switched over to the variable mode controlled solely by the rheostat.

Your problem is that the rheostat variable illumination has failed. The only thing the light switch controlls is the switch over and enabling of the variable dashboard illumination - since it switches over it likely works OK, Investigate the rheostat circuit? do the console light illuminate OK with the market lights on?

Focus in from this direction...

Alan

Ed Scherer

These dimmer rheostats are a common trouble spot. I'd recommend contact cleaner and/or DeoxIT, but make sure to get all the relevant contact points. Note in particular that for the −89 rheostats, the main trouble spot is often not where the wiper contacts the resistance coil, but rather the other end of that wiper arm where it pivots (the current has to pass through a tension washer; perhaps lube, corrosion, and/or grime at that point causes most of the loss of electrical continuity).

−89 and 90+ have significantly different rheostats. Based on my experiences testing them, they're often unreliable (I had a brand new −89 version that didn't work reliably at all right after I took it out of the package and bench tested it!)

For more information on trying to resurrect them (or even making brand new ones more reliable), see the following posts:

• images and cleaning notes for −89 dimmer rheostat (928.613.121.01)
• images and cleaning notes for 90+ dimmer rheostat (928.613.031.00)

Gregg K

Doh! I totally blew right over the pivoting contact area. I may pull it again and give it a cleaning. Meanwhile, I'm happy with what I've got. Just goes to show that nothing is ever simple, even if it is simple.

PS- this whole experience has reconfirmed my love of some of the German engineering. Right down to the screw that holds the dimmer in. You don't have to completely remove it to get the dimmer out, thus making it far easier to reinstall.