For the US 88 model, there is a black and gray wire and brown wire pair that goes to the lighter, and a gray and violet wire and brown wire pair that goes to the ashtray bulb. I hope that helps sort out your wiring problems.
As for the AC, the Haynes W124 manual has nothing on AC system controls. The non ACC W116 has slide controls so I wouldn't even bother. If you're interested, I can email to you a couple of vacuum diagrams out the W126 CD that might help your find the problem. <cover my a$$>These files would be for evaluation purposes only. You may not actually fix your car using information gathered from these files unless you buy your own copy of the CD.</cover my a$$> And anyway, there are enough similarities between US and non US cars to make the CD manual worthwhile to anyone with a W126.