Fear not the seat pot (potentiometer) How to rebuild one without removing it.

Yesterday, it happened. Went to put the top down and only the driver's seat moved forward. Passenger seat just sat there. The odd thing was that the top actually started to come down, but would have run into the passenger seat, had I kept going. In my case, I could still move the passenger seat with the seat switch.

Dollar signs swirled in my head.

FerrariChat to the rescue. It turns out that you can diagnose and repair a seat potentiometer failure for about $3.50 and get it all done in less than 2 hours. No trip to the dealer needed for re-calibration (in my case and many others).

What was going on in my case: I had a bad seat potentiometer. (breaking it down for those who are new to the subject). They're very small black boxes located one under each seat, which tell the car the position of the seat. They let the car know when the seat is far enough forward to clear the convertible top as it comes down, and also stop the seat motor when the seat reaches the forward limit of its travel, before the seat mechanically binds at the end of the rails.

To test mine, I motored it to the forward position. My seat switches were still functioning, but for those who don't have working switches, the seat can be powered by applying voltage directly to the motor. Once in the forward position, I turned off the key, un-plugged the connector for the seat potentiometer (just under the front of the seat) measured the resistance between each of the three wires pink to yellow, pink to brown and yellow to brown. Then plugged everything back in, turned the key on and motored the seat to the full back position, turned the key off, unplugged the seat pot connector and measured again. Same reading. This is the classic failure mode for a seat pot. The seat moves but the resistance from the potentiometer doesn't change.

Once I had sorted out that I had a failed seat pot, I set about rebuilding it. Using the technique described above for testing the pot, I racked the seat back, removed the front bolts. Then ran it forward and removed the rear bolts. Then I disconnected the wires to the seat pot and the motor and pulled the seat.

The number below for setting the resistance only works if the seat is left in the forward position.

 

I set the seat down and prepared to rebuild the seat pot.
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Remove the torx screw that holds the seat pot in place
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Then rotate the assembly 90 degrees to the right and pry the upper half of the cover from the lower half. (by the time I took this, I had rotated it back to it's original position)
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Lift the variable resistor (this is the potentiometer) from the assembly. There is a little black plastic clip at the right hand side of the part that releases it.
Set the variable resistor aside for now.
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Lift out the gear/ball and little white socket. This is the part which will be repaired.
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The arrow shows where the plastic has broken. The metal ring provides tension and keeps the white socket clamped to the black ball. Once the plastic breaks at the tips, there isn't enough friction for the gear to drive the white part and the potentiometer no longer turns when the seats move.
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I didn't take photos of the next couple steps. Separate the white and black parts by pulling on them gently. De-grease the parts with alcohol and q-tips (will need to strip down the q-tips to fit into the socket). Apply a light coating of contact cement to the ball and the socket, set them aside for a couple minutes while you do the next steps.

With an Ohm meter, measure the resistance between the pink wire and the yellow wire. Now turn the potentiometer until this reads 4.4k Ohms.

 

Set the black gear/ball back into the assembly and bolt the assembly down with the torx screw. Slide the shaft part of the white socket into the variable resistor. Check the resistance again, and make sure it's 4.4k Ohms. Carefully slide the variable resistor and the white socket down into place without rotating them. The white socket will snap onto the black ball and the contact cement will bond them together.
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Snap the cover back in place and check to see that you're still at 4.4k Ohms (mine ended up at 4.42 and it was still ok. Don't know what the limits are here).

Install the seat, being careful to plug everything back in before turning the key on.

Motor the seat around to see that it works. Then test the top.

Note: if you do happen to turn the key on while the pot is unplugged, it seems to disable the seat, even once it's all plugged back in. If this happens, turn off the battery. Wait 20 seconds. Make sure everything is plugged in, and turn the battery back on. Sorted me right out when I made this mistake half way through.

I tested the top 5 times after I finished and it works great. Both seats do all the right moves.

Others have used epoxy for this repair, but I liked the idea of using something like contact cement, since it's rubbery and has some flex to it, in case the ball and socket don't go together perfectlty straight. If it starts to slip in the future. I'll go to something stronger. Also, I was in the mood for some instant gratification today, and contact cement only takes about 10 minutes.

Thanks to those who came before me on this one. None of this information is new. I approached a couple things differently (like not removing the pot completely from the seat), but the important parts all came from various searches of FerrariChat. This is just an attempt to put everything I learned today into one post.

I'm really grateful that FerrariChat saved my a$$ and my wallet on this one!

Total cost $3.50 + tax.

 

Thought I should post the sources of most of this information, since I'm sure they include details I have left out.

Repairing seat pots:
http://ferrarichat.com/forum/showthread.php?t=280190

Replacing seat pots:
http://ferrarichat.com/forum/showthread.php?t=131465

 

The seat bolts? Mine weren't that tight. To get at the front ones, I used a standard allen wrench. I put the long end into the bolt, then used the handle-end of a crescent wrench. Here's an example (torx wrench shown, but I used an allen)
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Thanks everyone for the kind words.

I'll be curious to see if everyone is able to avoid re-calibration with an SD. Every pot should work without recalibration if set to roughly the same resistance that it was calibrated to before. So far 4.4kΩ seems to be the consensus for the forward position. I probably should have measured my (working) driver's seat to see what the resistance was in the forward position, but I was reluctant to mess with the one seat I had that was working properly.

 

The potentiometer needs to be physically re-set to a lower resistance value to allow the seat to go further forward.

I would measure the resistance on the driver's side seat pot when it's all the way forward and try to match the passenger side to the same resistance when it's all the way forward.

In the non DIY version, this step would be done by taking it to the Ferrari dealer and using the SD2 to set the seat position.

One of the advantages of using contact cement instead of epoxy is that it's easier to take apart and re-set the resistance to an exact number. You can also re-set it without taking the ball and socket apart, but can only adjust it in discrete steps, and they might be too large.

 

Cool! Yeah, I think within an inch +/- of what the other seat does is about as close as you're going to get to perfectly matching the other seat. Glad it worked for you, in general, though.