This sounds like it will be in what Winnebagoconsiders the Chassis wiring that they buy from the chassis folks as a stripped chassis. They then build the RV part on top and onlyu provide info on th epart they add.
They show the section of wiring to the front top lights but do not even show the lower front lights as being there! I take your word they are there!
So that leaves us to guess a bunch on how they get power to the lower but the upper shows a 2 pin connection near the top passenger corner. Not something to chase if there are lower and they also don't work!
That is where we may have to start looking for things Winn doesn't show and chassis folks hold the info tight!
I don't know the Springer well but on a ford or Chevy, we would expect to find a box out under the hood where there are only chassis fuses.
Think what would be on a van chassis only with no RV on top?
Do you have asmaller booklet ion a bag of info that covers only chassis stuff?
That should come with the RV and "should" show where to find chassis fuses?
But I know they get lost over time, so maybe not there?
Maybe a close look for a fuse box out under the hood? Maybe a drawing or label on the insdie of the cover?
Maybe some Sprinter folks will come a long to tell you a better story?
Wish you luck but I suspect there is a blown fuse hiding somewhere that feeds both top and bottom front!