Our 2015 4WD Mercedes Benz Sprinter van's previous owner spliced a wire to the right headlight. They left the original dust cap off since it couldn't be used with the new wire. This let in a lot of debris. We bought rubber dust caps that can be cut to size from Amazon, we cut a notch for the wire and taped it into place (though the fit was snug already).

Hope this helps if you lost your dust cap or have new wires to accommodate.

Video on headlight removal:
   • How to Change Sprinter Van Headlights...