PeachParts Mercedes-Benz Forum - View Single Post

jay_bob · #2 01-05-2015, 04:54 PM

If your seats are the memory type then you may well run into trouble.

There are 3 ways the 124 seats get controlled:
- Non memory: the 12 V dc and ground wires go direct to the door switch from the fuse box. Each movement control directly flips the polarity of the voltage applied to each motor. This is the standard arrangement for all 124s from 1987 through 1995 that have non memory seats. This results in many heavy wires from the door switch to the seat base.
- 1st gen memory (1986-1990 IIRC): The power goes to the control box under the seat. Each movment control direction has a dedicated wire back to the control box. Relays in the box handle switching the voltage to the motors, and the motors have feedback potentiometers so the system knows where each motor is at. The door to control wires are thin because they are only logic level signals, not the actual motor current.
- 2nd gen memory (1991-1995): Similar to the 1st generation memory except that each movement switch has a different value resistor on it, and the control box reads the resistance value to determine which movement was requested. This cut the number of wires between the control box and door switch from almost 2 dozen to 4.

I would recommend perusing the electrical manual for the 124 to see how the different systems work.