87 W124 power seat stop working for days at a time, not a fuse issue
 

I dont get it, my power seats and power column will stop working for days at a time, then all of a sudden start working again. i replaced all my fuses with brass ones and it makes no diff. both seats, all functions, up, down, front, back, tilt, head rest, everything will go defunct, then all of a sudden turn back on?
Has anyone else experienced this?
Its a 87 300D

I had this issue several times. Try to replace seat adjustment switch first

l can think of a couple things.

The power seats on a 124 get their power from the K5 relay in the back half of the fuse box.

The relay coil is fed from 2 paths:
- when the key is on the power goes F2 -> diode (in rear of relay box) -> K5 coil
- when the key is off and either front door is open it goes F9 -> the two door switches in parallel -> K5 coil

The relay contact gets its power from X4 (the main power distribution point located under the dash on drivers side above the e-brake pedal). From there it goes through the K5 contact and then to the two pole fuse holder located in the relay area of the fuse box. These 2 fuses feed power to the front seats.

If your driver seat has memory then the power feed comes to the control box under the seat. If not the power goes out to the door and then to the motors from the switch assembly.

Here is what I would do:
- Check the two fuses under the relay cover.
- Check the tightness of the connection at X4 (disconnect the battery first, it's unfused power, and drop the drivers side lower dash panel).
- Check that the relay K5 picks up (you should feel it click with your finger on the case) when the key is turned to position 1. Turn the key off then check to make sure K5 picks up when each of the two front doors are opened.

Trying to see if the problem is with the relay coil circuit or the main power path through the relay contacts...