I had the same problem. Clean your contacts and get new bulbs.

William

One minute they worked and the next they were not.  My backup lights are not
working on my '86 Weekender.  I checked the fuse and the bulbs.  All are OK.
It must be the backup switch and this brings me to my question.  Where is
the darn thing?  I expect this is another reason to buy a Bently's Manual
and your right.
In the mean time thanks for any help you might provide.
Mike Allen