PeachParts Mercedes-Benz Forum - View Single Post - Rear windows blow fuse when operated from front switch

tinypanzer · #11 03-31-2017, 07:26 PM

Ok, I think I have a working theory. I think you have a bad switch, but not one of the ones you'd expect. There is a weird shared ground setup here and the circuit reverses polarity depending on window direction (up or down), and if one of the switches is failing to disengage from either leg, it could make a dead short.

The power also passes through the front switches on its way to the back windows. If you remove the front switch for the rear window, the rear window will not work at all. When you use one of the front switches, you pass power to the rear motor on one wire and provide ground to it from the other. The polarity of this changes depending on if you are rolling up or down. One switch failing to disengage fully could be causing this.

Here's a test I propose. Start by disconnecting center console switches. Disconnect all but the switch for the driver's rear window. If the fuse still blows, disconnect all but the switch for the passenger rear window and try again. If you wind up with it working in one of these scenarios, re-connect each of the center console switches one at a time until the problem re-appears. That will be your defective switch.