Couldn't find C124, but after unplugging centre console seat/hazard switches, I measured infinite resistance from pin 12 to ground. I checked the climate control and dash lights and all now work.

I have the switches on my desk. But I don't really know how to test them. It looks like 6 is the feed from the dimmer circuit and 4 is ground. Lighting appears to be through LEDs. I tried measuring resistance between terminals 4 and 6. Starts off at 0.00 which is disconcerting, but then increases quickly - 0.1 - -.3 0.5 MOhms and so on. Same for all switches.

Any idea if this is normal?

Diagrams here

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Graham
85 300D,72 350SL, 98 E320, Outback 2.5