The marker lights are part of the Ram Promaster Van and were installed by RAM.

You get them fixed or replaced at a RAM dealer (preferably a Ram Businesslink Dealer who sells and is experienced working on them.

Note:  This has been a known issue and TSB’s (Technical Service Bulletins) have been issued on it in the past.

(These are not a Winnebago installed item and Winnebago makes no changes to them.)