1990 Mercedes Benz 500SL Synchronizing Power Windows Service and Repair

If the power supply was interrupted (battery disconnected or low), the windows cannot be opened by the Express feature.
To resynchronize the Express feature:
Press the UP side of the window switch (to the 2nd detent, if present) until the
window is completely closed and hold for and additional 2 seconds.
Repeat procedure for each window.
Note: If vehicle is equipped with two way Express feature, each window may also
have to be resynchronized in the full open position as well.
Press the DOWN side of window switch (to the 2nd detent, if present) until the
window is completely opened and hold for and additional 2 seconds.
The automatic full opening procedure of the windows should now be restored.
Attached to this service information is a copy of Work instruction #256 which describes
the procedure for window adjustment on model 129.
Figure 1 Check proper fit and adjustment of window (arrows, positions 1 and 2, Figure 1)
with door and window closed The window can be adjusted at points indicated by arrows
in positions 3-10 in Figure 1 (see Procedure).
Procedure
1. Install hardtop, if removed.
2. Remove interior door panel (job no. 72-100).
3. Remove lower body protection panel (job no. 88-800).
4. Remove speaker group and air passage.
5. Remove protective plastic liner from door.
6. Remove inner and outer sealing rail (job no. 72-160 and 72-170, respectively).
7. Adjust door if necessary (job no. 72-050).

Source