I found this info doing a search on "sl320 harness". It was posted my another member. The harness has been an issue on some models.
I have a 96 SL320, and it has some little gremlins too. Everytime I wash the engine it goes into limp mode, I am told that it is from the moisture causing an arc in the ignition, the computer sees this and then set it to limp. I correct by shutting it down and re-starting.
I have friends in the MB club that have problems with the big black box that sits between the firewall and the passenger side windshield. When I got my car it had a crack in it, 2 others told me the same. This crack lets moisture into the computer box, that is where all the "brains" are for everything. Make sure there is no moisture getting inside, that it is sealed properly. When they put some of these together the harness connector inside was too high and caused the top to crack when bolted down.
Another problem with these cars is the wiring harness. MB made the harness bio-degradeable, so it is already weak, if you get it wet it makes it worse. Usually the engine harness will go first. Because of the heat and exposure to weather conditions. With your Top controls goofing up and your braking systems, I would recommend that you take it to a dealer and have them hook it up for a diagnostic. It seems like the harness between your firewall and your windshield could have problems, you will see where they all meet up at that black box. The engine control, the soft top, the cruise, everything is in that box. Be careful when checking these out, some have said all it takes is a little twist and the wires arc/ they don't break, just the insulation around them, causing them to arc or ground out. This makes it fun when trying to find a problem. Overall this is a great car, so don't rush out and sell it. If you are not an MBCA member join, you will get free tech advice and you also will get discount at dealers. goto
www.mbca.org. Good Luck.
Regards,
Brian