1) Removal and disassembly of the donor seat to free the W126 seat cushion

Repositioning the W126 electric seats in the yard (to allow access to the 4 bolts that mount the chair rails to the floor) requires a 12 to 18 volt DC power source and a pair of leads. (Fig. 5 & Fig. 6)

Jumper batteries may be prohibited in the yard.
However, two fresh 9 volt batteries in series or the power pack for an electric drill can also work.

Move the seat forward to reveal the rear 10 mm mounting bolts.
The bolts are easy to round off with an open end wrench.
They are difficult to grip securely because of the awkward angle they insert into the floor.

A Ό inch drive socket wrench with a universal (or wobble) adaptor can work.
I was able to borrow a 10 mm long-handled, swivel-headed micro movement gear wrench (I think it is the best tool for this job).
Remove the rear bolts. (Fig. 7)

Next, remove the plastic cover on the seatbelt rail guide anchoring bolt to access and remove the bolt. (Fig. 7)
Reposition the seat rearwards.

Remove the front plastic anchoring bolt covers (if they are still present and not broken off) under the bottom fore-aft seat adjusting track to access the 10 mm front anchoring bolts.
Remove the bolts. (Fig. 7 & Fig. 8)

Next, unplug the three chassis wiring harnesses that connect at the front right of the seat, below the seat cushion and near the front right anchoring bolt. (Fig. 8)
Trace the seat belt warning buzzer harness from the bottom of the seatbelt receiver to its chassis harness and also unplug it.
Also unplug the vacuum connector from the orthopedic vacuum supply line under the chair.

With all five anchoring bolts removed, and the four chassis wiring harnesses unplugged, and the orthopedic vacuum supply line unplugged, the whole seat can be removed from the donor car.

To save some money, if you only want the seat cushion, you can disassemble the seat to free the seat cushion in the yard.

To free the base of the seat cushion, you need to remove the two upper tracks that control the seat fore-aft position.
These are held in place with three large Phillips head screws that can be very tight. (The rearmost ones are visible in Fig. 7)

Position the chair upside down on some soft carpet or cardboard and wedge it against an immovable object so it won’t slide when you remove the three screws.

If the screws are stubborn, have the weight of your body directly over the screwdriver in the palm of your hand, and with your free hand grip the screwdriver handle with large adjustable pliers (ie Channel Lock brand of pliers) to give enough torque to break the screws loose.

The middle screw can only be accessed through a hole in the bottom part of the track assembly.
Use your battery pack (as needed) to expose the positions of the screws to allow their removal.

After detaching both rails, (Fig. 9) the next step is to unplug the three backrest motor harnesses. (Fig. 10)

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022