What's the best way to trouble shoot this problem? on 1990 Mercedes-Benz 300E

Couple weeks ago while waiting for my daughter to get out of class. I sat in the passenger seat to recline and relax and the seat won't come back up but, it will go down. This is the first time this has ever happened. What could be the cause of this and how do I trouble shoot it?

Asked by for the 1990 Mercedes-Benz 300E
Probably a bad contact on the switch. That's what I'd check first.