First thing I would do is check fuses. Even if they look good, if they have never been changed int he car in its years, then might as well do it.
Its a minimal cost, and sometimes is the easiest way to fix a problem.
Though I would lean towards searching for OVP as this little relay will cause many many problems if the unit is faulty...
Do the research on OVP definately and if the fuses have never been changed int he car, might as well spend the few $$ to change em all.
I changed all of my fuses in my car for new ones the day I bought it.
'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.