91 500SL Instrument Cluster Lighting
 

Have a problem with the instrument cluster lighting, climate control lighting, seat adjust backlighting, console lights - working for a while, then cut out. All gauges working fine. OK, I've pulled the cluster, replaced the 470uf capacitor, touched up any suspicious solder joint, scrubbed all connector pins on the PCB to remove as much oxidation as possible (replaced bad temp display LED), sprayed out the connector plugs - reassembled and installed. Everything worked fine the eve I re-installed - drove around for an hour to heat it up - no issues. Took the car to work, left in the sun (about 70F) for the day, got in the eve to leave and same problem - no instrument cluster lights, backlights for seat adjust, climate control, console, etc.. Get in the car this morning after cooling down overnight and I've got all the lights. Somewhere, it's got to be an intermittent connection...any advice on how to narrow the search??

Sounds like you really did your research on the instrument cluster. Nice to have the backlight working on the LCD temp. A long shot issue might be as simple as a bad fuse. You'd think they either are good or they are not. But if you have the original aluminum fuses, they can be intermittent. The aluminum contacts oxidize. They make brass fuse kits to solve this problem. I'd use a volt meter to check at the fuse box when the lights aren't working. Also, there is a common "ground" point stud in the console behind
and below the radio, but if the radio works, thats unlikely an issue. Maybe somebody with alldata can post a wiring diagram.

You may want to just bypass the cluster's control of the lighting inensity as mentioned here: http://www.benzworld.org/forums/r129-sl-class/1354321-interior-lights-intermittent-91-500-sl.html#post2710474.

Don't know if this is possible, but on some volvo models the ignition switch caused this problem. the next time it happens, jiggle the ignition switch to see what happens.