Clock only works with ignition on!
 

Any suggestions?
The clock in my '88 420SEL stops when I turn off the
ignition. While driving it keeps time just fine.

I have not yet checked anything. Where do I start?

Thanks in advance.

I'd check the fuses. There's one that feeds the instrument clock, cigar lighter and various stuff on my 300E. And these fuses drive me nuts as they develop bad contact in my car. I am sure theres something similar in your 420 too. Just check the fusebox lid for which fuse it is, and wiggle it around a bit and see if it helps.

I'm ready to replace my fusebox this weekend with ATO fuses.

http://ow.no/mb/w124/pictures/engine...justcables.jpg

On the back of the instrument cluster there is a lone wire plugged into the back near the clock that provides a constant 12v for the clock. This wire is seperate and not bundled with any other wires. Its easy to locate. If the fuse were gone it would not power the clock even if the ignition is on.

Pull the instrument cluster and check for voltage on this wire. If none, then you have to back track to the source to find the interruption.