If by "back" you mean the part facing the rear of the car as opposed to the other "back" that faces the engine, then the wire you see there contains the rack positioning circuit and the rack position feedback circuit.

Essentially, ECU says "rack move forward" and the feedback tells the ECU "yep, it moved".

Now, it is possible to run the car with the side cover off the IP. This way, you can verify that the rack is indeed moving. It should do a full cycle when you switch the key on then settle down to a position about 6mm from the resting position.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250