Hey guys,

Working on my 1991 500SL that has some soft top issues. I bought the car a few weeks ago and the soft top (and hard top obviously) didn't work. Upon turning the ignition on the S84 soft top switch bulb does not light up at all, and I believe it should stay lit for approximately 3 seconds. Pushing the S84 switch forward or back has zero effect and again no bulb lighting up. Upon reading codes from pin 10 on the X11/4 diag connector I can read codes from the RST module, but the bulb on the S84 switch does not blink in parallel with the LED on the code reader. On this subject, I did have a code 7 for "limit switch, right locked, soft top fabric bow" along with a normal code 20 for the hard top recognition when I had it on. I cleared the code 7, and now after taking off the hard top off manually I have no stored codes (just the 1 blink as it should be). No other codes stored for any other modules.

Also when I first bought the car, the dinging sound for the top not being fully engaged in the locks had come on shortly after driving it. Of course, as soon as the car stopped the dinging stopped but as soon as it started moving the alarm sound would come back on. Using the factory top wrench, I attempted to lock down the front locks (above the windshield) and the right passenger lock must have been not fully engaged since after tightening it down the noise stopped. The roll bar is functional and operates at a normal speed. Both driver and passenger windows work fine. So the RST module does have some functionality and is working partly correctly.

Through StarFinder and WIS I found some diagnostic information for the N52 RST module. I started going through the information I found and checking multimeter readings at the N52 RST module connectors. For pins Y1 and Y2 of the N52 module (pins 1 and 2 of the large Y connector) I found that there is 11 volts (actual reading is ~10.9v) present at both pins without even touching the S84 switch.

These pins are both for:
Y1 pin (blue/white): "soft top close signal switched ground input, initializes process to close soft top"
Y2 pin (blue/black): "soft top open signal switched ground input, initializes process to open soft top"

With test values of:
Y1 pin: "Push S84 back: Approx. 12 VDC"
Y2 pin: "Push S84 forward: Approx. 12 VDC"

This left me a little confused as to how both pins are reading ~11V without touching the S84 switch at all. It seems that according to the wiring diagram (posted below) the S84 switch is fed power from the S83 switch (roll bar switch) which is somehow connected to the power of the S21/2 switch (right side window switch). The S84 switch ground is also all connected to S83 and S21/2 to a final ground of W19. It seems the switch should then feed 12V from these sources to pins Y1 and Y2 when being pushed forward or back to initialize the soft top procedure. Obviously this is not what's happening in my car. Can someone explain how this could happen? Is the switch potentially bad or could something in the RST module itself cause the pins to be fed power internally?

I attached an image of the corresponding parts of the wiring diagram, along with the test procedures from StarFinder, and finally an image of the N52 RST module pins I am talking about (Y1 and Y2).

Thanks in advance!
Austin

 

I determined that the Y1 and Y2 pins are expected to have power at all times, and are grounded by the S84 switch.
The issue still stood with my S84 switch not doing anything (no change in Y1 or Y2 voltage when switch pressed forward or back).

Replaced switch with new one from the dealer. Some progress but not quite there yet.

The new switch does not light up at all still. No light upon turning on ignition, none pushing the switch forward/back, and none when reading codes thru X11/4 pin 10.

But, the switch does cause the hydraulic pump to activate now so it does partially work. I could hear the rear tonneau cover trying to work I think? Or something back there was trying to work at least when I pushed the switch forward. I held it for around 10 seconds to see if it would do something but it didn't.

When I first tried, the windows were already rolled down and the roll bar was down. So, I expected the next step to be the tonneau cover opening.
After it didn't work once I rolled the windows up and put the roll bar up. Pushing the switch did still activate the pump but windows did not go down, and the roll bar did not go down. So not sure that the full procedure is happening?

I opened the door to find a puddle of hydraulic fluid on the passenger side behind the rear tire. Obviously a big leak from one of the cylinders right above the battery (picture below).

Any ideas on why the switch is not lighting up as it should and to why it doesn't seem like the full procedure is happening? Looks like pin Y33 is connected to the bulb in the S84 switch. Is this something I should look at?

Edit: Forgot to include that I read codes after trying the top as well. I got code 20 (hardtop recognition) when before I just had code 1 (nothing). Hard top is not installed.

Thanks