Starter Override Switch....
I got a momentary pushbutton type switch, a fairly large one, since the solenoid on the starter actually takes several amps. I might have gotten the switch at a good hardware store, or some electronics store or from ebay; I cant recall. The switch has to be the kind that is "normally open", that is its only closed when you are holding the button depressed. The switch has two wires coming to it. I ran a wire (about a 14 or 12 awg stranded wire) from the small terminal on the solenoid that sits atop the starter, across behind the engine and in through the grommet that is close to the brake vacuum booster - about at the 2
.m. position. I actually ran a few wires at the same time, but I only needed one for my starter 'over-ride'. I got the 12 volt supply I wanted by splicing into the wire to the cigarette lighters - which is easiest to do working from the driver's side of the console. Since the lighter is only powered when the ignition/accessories are on, the switch wont do anything if you push on it when the ignition is shut off. There is a small nut on that small terminal on the starter, and unscrewing it, putting my extra wire on it, and getting the nut snugged back down again took a few minutes. The small nut might be an 8mm, (or 5/16th inch), or it might be a 10mm I cant recall. The switch was a lifesaver for us, but there is a danger to it. It bypasses the "wont start unless transmission is in park or neutral" function of the range-sensor. So if you have the shift lever in Drive, the ignition on but the engine not running....then pushing that switch will launch the car. Very bad when you want to carefully back-out of a parking space at Walmart.'
Now I need to add a different switch to my 95 SL2, for the same reason I had to add one to my daughter's 98SL2. The wipers would start to work when the ignition was switched on, even though they were in the off position; and sometimes they would not stop when they wanted to shut the wipers down after a rain. My switch just cut off the power to the wiper motor. It also stopped them wherever they were - so you had to twitch the switch to get the wipers to the 'parked' position.
Something you might try with the door lock and unlock switches:
There are two relays in the upper-rear corner of the fuse box on the passenger side of the console. These have to do with the door locking/unlocking. With my 96SL1 I had one of them that would periodically go nuts ---- and either make the locks chatter, or drain the battery overnight. A couple of times the car locked me out when I just shut the door normally! I yanked out the two relays, and the misbehavior stopped. I had individually to lock/unlock the doors, but since I seldom had passengers when I used that car, it wasnt much of a sacrifice.
The only thing an SL2 has that I want on my SL1 is the cruise control.