Several months ago I lost the function of my driver's seat backrest (will not tilt forward or back) my indie checked the switch (ok) but found that the power wire has a break in it somewhere, the question is where? He explained that this repair could be very expensive in terms of locating the break and that other surrounding wires may be in similar shape. does anyone know the locations where these wires typically break (is there a "typical" location?) Thanks!

What car? And quickly before Brian notices

I would start by pulling the switch knobs and spraying into the switch liberally with Caig DeoxIT or a good contact cleaner. You can't use too much of that stuff.

If there's a broken wire, I'd guess the break is in the area of the door hinge. The cabling for the backrest goes from the fixed part of the seat track to the seat bottom that slides and the backrest that pivots os there are other places wire can break due to motion or pinching. You'll have to pull the seat and cut into harnesses to check the wiring in the seat. Hopefully you can narrow it using a continuity meter.

Sixto
87 300D

ooops, thanks '82 300SD

I could almost guarantee that if the switch is clean and good then any broken wires are at the door hinge area. This is very common and I have had to splice in new sections on almost all the wires going through that area on my car. Remember your car is 26 years old and every time you open the door you bend the wires.

__________________
1983 300SD
200000miles

sounds like a lot of work! So splice from where wires exit door into hole in jam? Thanks! Time to get out the aligator clips!

I just took off the door panel and the panel under the dash and kick panel, this takes 15 to 20 minutes if you do it slow and carful. I cut into the wire in the door and then fish the wire into the door jamb and down to the channel on the floor where it is easier to work on.
If you cut the wire in the door and add the new wire to the end of the part going to the door jamb you can use the old wire to pull the new wire through.

__________________
1983 300SD
200000miles

If your car doesn't have memory [correction] seats, the switch sends +12V through an orange wire to recline or +12V through a gray wire to set upright. If the backrest doesn't move in either direction, I'd suspect a bad switch vs those particular 2 of 8 wires failing, or a problem with the motor, cable or gear drive in the backrest.

Set the front of the seat as high as it will go and look for the 8-pin connector at the end of a cable coming out of the carpet going into the seat base. Pin 1 is the orange wire, pin 2 is the gray wire.

If your car has memory seats, the switch will send ground rather than +12V signals to the seat. There will be a 14-pin connector into the seat base. Pin 13 is the orange wire, pin 14 is the gray wire. I'm pretty sure the ground source to the switch is maintained even is the 14-pin connector is disconnected from the base.

Sixto
87 300D