Well, Maustin...are you prepared to make a bit of an investment in your Tuna Boat! I jokingly refer to my '86 420SEL "business Blue, 90K" as the "Tuna Boat"
1st - Under the hood, directly in front of the Driver's seat in the fuse box....all should be labeled, that's where you will find your wiper/fuse/relay.
2nd - remember that you have bought a very large heavy sedan and with that comes all the trials and tribulations that are inheritant with the SEL class. i.e.,
ENGINE: Fairly bullet-proof but has a few bugs, such as the timing chain guides. They are notorious for being brittle, turning brown and breaking, resulting in a very expensive fix repairing the mutiple valves in usually takes out in the process! Consider these upgrades to help it's overall well-being: MB air filters changed religiously (K&N's don't impress me on this particular car), try Mobile1 synthetic oil for your next change, flush the radiator, get a decent battery (try consumerreports.org for the latest ratings), consider TimeValve SS cat-back exhaust system as a replacement for your current system, but be aware that their welds are debatable at best ( just sloppy production work) be prepared to have to reweld questionable joints in the system! Remember, you have a combo cast steel/aluminum engine and things do "move" so watch for gasket leaks on various components!
SUSPENSION: Remember what I said about the TUNA BOAT joke?
Front-end work is a mainstain in revamping your ride! Upper ball joints, tie-rod ends, swaybar bushings,steering linkage & steering box leaks, shocks; all need to be attended to! Lower ball joints are a costly endeavour. The SEL ride can be improved in terms of cornering (the tuna boat wallow!) by using lowering kits and yellow Bilsteins but you will sacrifice that "sedan-type ride" !
BRAKES: Stopping such a heavy vehicle requires some serious braking, so be prepared for the following: rotors - warpage is their downfall, don't turn'em ever though MB says a certain minute amount can be, replace'em with ATE brand or whatever MB calls their OEM that paticular year! Pads -squealing is all to common! Once again, ATE pads or whatever OEM brand could benefit from having all right-angle edges chamfered, score the middle of the pad a hack saw and using only blue MB paste applied properly!
TIRES: To each his own on this topic, living in Montana, I use Pirelli P6000 Veloce 205/65 R15 92H M+S during the summer (love'um!) and studded whatevers during the serious winters! Others like the Michelins! Consider a four-wheel tire-on alignment from a dealer.
ELECTRICAL: God Bless German engineering! Talk about a wasp nest! Going to a dealer and having them plug in the Lambda tester for a seroius system goin' over is a good place to start! Self-diagnostics is another conversation in itself! Your original key should have a little red bump/nip on it that is indicative as the "main" key that sets the alarm, invest in a new dealer-ordered original key based on your VIN! Your locking system is a rather complex vaccuum system you will need to learn about.
Final words of advise!
KNOW YOUR SYSTEM, BE THE SYSTEM! INVEST IN THE SERVICE MANUALS! READ THEM! EDUCATE YOURSELF AND YOUR FRIENDLY LOCAL MECHANIC! Now that I got your attention via YELLING, the above is mandatory if you truly what to live and love your SEL! Shop wisely....nothing is "cheap" on this model,i.e., try FastLane (this site, )Ebay, Performance Products, etc. The MOST important thing I could possible advise you of is this website! Truly the most friendly, helpful, talented bunch of folks I've had the previlage of lurkin' around !
90% of all your questions you have or will have can be answered here by learning to navigate the past threads/replys/topics......I dare you to type in "420SEL" and spend the next two hours learning how to hate/love your tuna boat!
Trust me when I say I've only touched the surface of SEL info! Remember not to hold me responsible for the above info, opinions are like --------, everyones got one! ROTFLMAO!
Business Blue, 90K
TimeValve, Pirelli Veloce
Clear Turn Signals -Bosch