Someone pulled the rod off that joins the front seat motor to the side bit that moves on my BMW Z3. The other side still moves but when I put the rod back nothing moves! Help

The adjusting lever for seat position is not locking into place. On the bottom of seat are runners on each side with holes in them that the adjusting lever tabs will lock in and hold seat in place. The seat slides on the runners if those tabs are raised. There is also a connecting wire or rod from the lever to the other side of seat so when lever is pulled up, tabs on both runners are raised for seat to slide. Something is keeping the tabs from locking into the holes on the runners in your car. Maybe the adjusting lever is broken somewhere, or the wire/rod came loose, or the lever is just dry and sticky and needs a shot of WD40 to loosen it up. If you can't see it and fix it with seat in place, then pull the seat back off for the repair. Good luck. Post back if my explanatiopn is not clear or you still need help.

a leak in a hose or a bearing on a motor

could be. could be a switch or motor. different switch contacts for up/down along with different motor

motor and/or switch

This is a common BMW problem before giving to a mechanic try looking at the mechanism to see if any bolts are loose or missing,you might find the bracket is broken or torn and needs to be welded or replaced,the job is relatively easy but be carefull because of the SRS system if not sure give it to an expert.

It can also be theseat motor since there is seperate motors for up/down & forward/backwards. You can test the switch to see if you are getting power to the connector on the motor by using a multimeter.

If there is power to the motor, I would remove the motor and give it a tap on the ground. Alot of the time the motor is fine, and the tap will free it up again. If it doesn't work you may be up for a new seat motor. Giving mine a tap solved the issue with mine.

make sure the arm is connected from the conv. top motor to the convetible top. It is located behind the drivers seat by the door jam.

Bushings in seat are shot. See this link: http://www.youtube.com/watch?v=DM4KSnA58EI

the first thing to do is remove the plastic skirt around rhe seat,to do this remove the seat movement knobs by prying them off with screwdriver,gental steady pressure works,then remove the screw in the rear( back seat compartment),three screws at seat switches and the side skirt will pull out (four tabs are connected to the mating plastic pieces,pull outtoward you). two screws hold the front skirt on these are tough to get to they are at an angle. with this skirt removed you can get to the motor,
three screws remove the the motor (Isuggest unplugging motor,small connector) on each end of shaft are retaining bushings rotate them toward the back and they will disengage,you can now pick up the motor and the the shafts will come out with it.these shafts disengage from the motor and should be kept seperate (greasey)
I used a R2 square drive bit (the driver used to install deck screws) to find which screwdrive is jammed, I adjusted the other one to its front stop with square driver bit the worked the jammed one back and forth mostly toward the rear and it worked free.
I adjusted this one to the front stop and reassembled the motor,shaft(make shure to snap retaining bushing in place)reconnect motor connector,all plastic skirts AND NEVER ALLOW THE SEAT TO TRAVEL TO ITS FRONT STOP AGAIN. (4HRS)

its the dreaded seat rock syndrome, plenty of fixes on the forums, basically you have to replace spacers in set drive mechanism. I did with the help of a friend after ordring bushes and it was quite easy.