Hello all. I am in need of your sage advice. I believe I have an electrical problem. Here's what I know so far:

• It's a 1986 300 SDL
• I've owned it for a year and a half
• Love it
• The rear passenger window has never worked since I bought it
• The drivers switch was always kind of flaky (it would stick up or down, but always worked)
• Last week the window went down, then up, then didn't move
• I replaced both the rear passenger switch and the drivers switch
• The rear passenger window made some odd noises, but didn't move. I suspected a bad motor, stripped gear, or stuck regulator
• I'll deal with that later
• Drivers side window went down 1/4" and stopped
• Driver side window would not move after that, suspected motor
• Plugged new drivers switch into passenger window, works great
• Pulled door panel, tried to get reading with multi-meter
• Checked fuse box (should've been a lot higher in the list)
• Learned that drivers window and rear passenger window on same fuse
• Fuse was blown
• Replaced fuse
• Disconnected driver's motor
• Fuse blows instantly when switch is depressed, with motor disconnected, when trying to test leads with multimeter

Wiring in the door appears to be in good condition. I don't really know where to start. I would trace the wiring back to or from the fuse box but once it goes into the door hinge I have absolutely no idea where to go from there.

When you disconnected the driver's door motor, did you disconnect both leads or just one of them? Did you leave the wiring harness connected to the plastic insulator in the door?

I'd suspect a chaffed wire either in the door or in the hinge area.

It's also possible (although pretty rare) that the plug that connects to the switch itself could have a wire shorted inside of it. It requires a perfect storm of events to have this happen, but it DID happen in the rear driver's-side door of my SDL. Had the switches out to service the regulators, and when I reinstalled them, the wires had just enough insulation stripped back to allow 2 of them to just barely touch inside the plug. I wound up taking the plug apart and adding a piece of heat-shrink tubing over the offending wire.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I disconnected both leads. I held the leads coming from the door hinge separately while in contact with the multimeter and depressing the switch. I did not think to screw them back to the door/plastic harness; I didn't think it would make a difference.

I'll admit that electrics are not my strong suit.

I had the thought just before I checked this thread again that the plug between the switch and the harness could be the issue. It was the only other thing I could have potentially, maybe, damaged when pulling the switch from the console. The switch I pulled was most definitely broken. It wouldn't 'click' into it's down position, the exterior plastic of the hinge was broken.

Are you certain that the leads weren't touching when you had them out? If you did, it's a dead short when you hit the switch.

Screw the wires back down on their respective posts and repeat your test, see if it still pops the fuse. If it does, you know that you have a wiring fault somewhere between the switch and the wiring post.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

I checked the plug/connector to the switch. Everything looks normal. All of the insulation tubing went straight up to the soldered connectors and there were no visible shorts, or damaging to the insulation or wiring itself.

I am positive they weren't touching, I tried it twice. Although I haven't repeated the test with the leads screwed to the door...I only have one 25A fuse left. Keep in mind that the original fault was a blown fuse, with everything connected as it was, before I took it apart.

I tried my hardest to inspect the leads where they go through the door hinge. I took the trim off the bottom of the dash and dug around trying to find exactly where those leads come through. As far as I can tell they're all bundled up with this fabric tape; I cant get eyes on where exactly the harness comes from the door through to the frame.

I read in an earlier post that the #17 fuse provides power to the window relay (with the key in the run/off position) which then sends power through the C and D fuses, and then on to the switches. Since the fuse blows only after I depress the switch to send current to the window motor, then the fault has to be between the switch and the motor, right?