The easiest and quickest thing you can do is get a 12 V battery and apply power to the vehicles original battery connections, then move the seat with the door open. If you have access to a computer UPS they all use small 12 V gel cell batteries that are great for this, also Home Depot sells replacments for about $15 each. Theses gell cells are about 4" X 4" X 3" and weigh a pound or two. Eight regular D cell batteries can be taped together in a 4 x 2 configuration with a short jumper connecting the stacks at one end to create a 12 V pack also.

This is from an earlier post to a different thread with the same question!

"Under the driver's seat is the memory module, at its front top edge it has connections for the seat switch (a 14 or 16 pole rectangular connector shell), the power connections (a 4 pole square connector shell), and a second square connector(this has the head rest control and something else I don't recall at the moment, in a four pole square connector shell), at the rear of the module are four square four pole connectors, one for each of the seat base motors and one for the seat back motor.

Each of these motor connectors has four conductors two are power to the motor and two are position info from the position potentiometer attached to the motor shaft. I don't have one in front of me at the moment so I'm not certain but I seem to recall that there are two different gage wires used for the two functions, the heavier gage for the motor power and the lighter gage for the position signal. There may actually be different size electrical contacts in the connector shell, I just can't be sure at this moment. One can easily look at the wiring coming from the electric motor and note the color code then open the four pole connector shell and note the position of those wires.

It is not the easiest but I have on numerous occasions; usually when a switch, memory module, or wiring has failed, reached from below and behind the seat unplugged these individual motor connections and used jumper wires and a 12 volt source to move the seat base enough to access the 4 bolts securing the seat base to the chassis. As a result I've also constructed an abbreviated wiring loom with a seat switches , power, and ground connections that can be used by unplugging the vehicle's seat wiring harness at the front of the memory module and plugging my setup into the module's connections then attach power and ground sources. I can then hopefully move the seat independent of the vehicle's system; this is also an easy way to begin the diagnosis of seat switch and seat switch wiring issue possibilities. If the seat still does not function properly it’s likely a memory module, motor or cable issue inherent to the seat or its' base itself. This setup also works great if you’re ever retrieving seats in a bone yard. I've used it to test some extra seat switches for functionality also.

Early 126 chassis vehicles without seat memory function are wired directly from power/ground, through the door mounted seat switch to the seat motors. In this case the connection under the seat can be unplugged and power and ground applied to the particular pair of wires and a functional motor can be operated. Wiring for the motors is like colored wire pairs i.e. purple/purple-white striped and located in parrallel adjacent pairs 1/2, 3/4 etc. in the connector shell.

124 chassis seats have a couple different generations ending with the last generation having the integrated convenience module and integrated micro switch controls, but the first generation is similar to 126 Gen II."