E36/7 Z3 (1996-2002)
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z3 Seat Swap DIY--older seats into newer car
Recently, when I bought second-hand black leather Z3 seats to replace my blue leather seats, I discovered that the electrical wiring had changed during the course of Z3 production. I'd need to rework the electrical wiring if I wanted seat adjustment, heat, and occupancy sensors to work correctly. After many months of stalling, and occasionally taking another befuddled look at the wiring, I decided to just dive in.
Wiring diagrams were of no real help, since the wiring colors didn't match what was present on the seats. I purchased a complete wiring harness in the hopes that I could scavenge the needed parts. In retrospect, that wasn't necessary, but it did help me determine which wires on the seats connect with which wires in the car.
I'll be the first to admit that I'm no wiring expert, and I offer these instructions simply as a helpful guide to you if you're contemplating the same mod. There may be other approaches that work better, and these instructions may not pertain to all seats and all year vehicles. In this case, the seats are 01/97 production and the car is 04/2001 production. I believe the wiring changed in 04/99 with the 2000 model year cars, though there may have been other iterations along the way. Also, I believe the ///M seats maintained the earlier wiring throughout production....
~ 10mm, 13mm, 16mm sockets w/wrench
~ adjustible wrench
~ blankets or towels to place seats on (they'll be upside-down alot of the time)
~ wire stripper and crimper tool
~ butt connectors, blade connectors, wire nuts, or soldering tools
~ portable lighting to see under seats
~ plenty of workspace at the side of the car
~ several hours to complete the task
Use the power adjuster to raise both seats as high as they'll go--this will give you more working room under the seats later on. Slide both seats back far enough to expose the nuts on the floor at the front of the seats' rails. Use the 13mm socket to remove all four nuts (two for each side of each seat). Next, slide the seat forward to expose the nuts at the rear of the rails. If your seatback is reclined, release it to full upright position to get better access to the rear. These nuts will now be removed with the 16mm socket. Now use the adjustible wrench to remove the bolt that holds the seatbelt to the seat base, and in the case of the roadster, work the strap out of the seatbelt guide at the top of the seat.
Disconnect the negative battery cable using pliers or the 10mm socket. Make sure you have your car's stereo code #--once the battery is reconnected, you'll need to reenter the code to use your stereo.
Tilt the seatback rearward as far as possible--this will allow better leverege for working under the seat, and also easier removal from the car. lift the back of the seat forward toward the windshield and get in behind it with lighting so you can see where the connection from the floor meets the seat connection. It is a yellow and black boxlike plastic structure that is fastened to the seat bottom. You can twist it to unfasten it from the seat. Once it's unfastened, the wiring can be disconnected by pulling on the black plastic piece on the side labelled 'a' in this image (The connection is shown already disconnected):
Here is an image of the connection that comes out of the floor (already disconnected):
Remove the seat from the car being careful how you lift and swing it out--It's easy to gouge your sill plate or center console. Set it upside down on the blacket or towel for easy reference to its underside. Set the replacement seat near it so you can compare the connections.
Remove the black plastic 'caps' on the floor's yellow connector for easier access to the wiring. Remove the cap on the seat-side connector as well.
Step 6: Passenger Seat only
Look at the underside of the replacement seat and you'll see the "seat occupancy sensor" which is shown in the following image. This needs to be connected in order for the seatbelt tensioner to fire and passenger side airbag (if equipped) to go off in event of an accident. The airbag indicator lamp will light up on your instrument panel if this is not connected when the battery power is restored. You will then have to pay for either the reset tool or a trip to the dealer to reset it. The driver's side doesn't have the occupancy sensor--the car assumes there is a driver present in the event of a crash. This image shows it disconnected--a white plug inserts where the arrow is:
On both replacement seats you'll see connections like the following:
The black plug is for the heating feature, and the white plug is for the seat motors. Because I had bought a separate wiring harness, I was able to salvage the parts that plug into these and make the following connection using butt-connectors (you can use blade connectors, wire nuts, or solder if you prefer). If you use butt-connectors, gentle pulling will ensure that you've crimped them sufficiently.
As I hope you can see, I only cut and rewired what was necessary to make the circuits complete. Some of the wiring from the old seats was compatible with the wiring in the yellow floor connector, and I plugged those seat wires right into the yellow seat-side connector as shown is this image (the central three blocks of wiring in the connector):
The outside blocks of wiring--one at each end--are what were converted to the old style plugs.
Place the replacement seats back into the car and get in behind them to reconnect everything. Reconnect the battery cable and test your connections.
I don't know what some of the connections were for, but none of it was redundant, and they've worked well since completion. This isn't the complete story, as I've forgotten some details in the 2 weeks since I did this. Questions, comments, or corrections are welcomed, but please post replies to the following thread:
Last edited by cngizbleevng; 01-14-2008 at 08:32 AM.
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