Blower won't cut off after I took the key out

okay Mercedes is Difficult to get to the right answer with, but am going to have to say a relay...or and undervoltage condition created by a battery that's older than five...and a corroded connection at the MAIN ground...follow the black battery cable to where it attaches to the frame...wirebrush 'till shiny...that lug and that territory that it bolts to~ with refreshed ground the relays should start working again normally....actually tried to "peg" this part...and even rockauto.com (my dependable source what has EVERYTHING for near every model...can find out if this part exists in reality or just one of my gearhead fantasies....but here's a relay...honestly do not think that we will need it once fresh grounding to the chassis/engine is established.....also there's a 1/0 battery cable leading to the engine block (near the alternator) disassemble and give this connection a scrub for good measure as well....this connection is so the fuel injectors and engine startermotor can see proper grounding tooo~

thee-lah~

you know I only imagined that this part MUST exist...trackin' it down was not easy...actually had to take a picture of the screen so that you'd believe me....relays....if they have enough juice normally do okay...except where a shorted load is concerned...then simply pluck the relays and give them a sniff....if burnt, that's the one to change out~

As a side note to judge_roy comment, does your A/C system have a button labeled "REST". ? On the 07 SL's if this button is pushed, it turns on the fan motor after the engine has been turned off. The purpose is to provide residual heat or ventilation to the interior for up to 30 minutes. Seems like a dumb option (especially in Florida).

I put a new belt on my 2006 Mercedes Benz R350 and now my cooling fan won't go off when I cut the car off