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250 Posts
Discussion Starter · #1 ·
With more imminent weather and the prospect of more cold bum on leather seat, I decided after 3 years of no heat, enough was enough - I tackled the driver's seat on the Anniversary to fix the heat pad. Using the usual forum info (have to say, Saabnet was particularly useful), I found a break in the loom close to the back of the seat squab (near the thermostat), and after a quick 5 min soldering - warm bum again!!!!

Have to say though, as a first time job the whole thing took me about 2 hours, from removing the seat from the car, getting the seat clips off and fault-finding. Hopefully the soldering will last, but if it happens again, hopefully it'll take half the time.

The weather can go sub-zero now - I don't care!

11,343 Posts
Excellent. Surprising how much you miss heated seats when you don't have them. Can make winter leather unbearable.

214 Posts
Don't suppose you have the link handy for that fix? Both my seats don't work in the bum warming dept!

250 Posts
Discussion Starter · #4 ·
I can't remember which website I got this from, but I followed it pretty closely and it worked for me:

Quick check: With the ignition switch in the Run position, you should be able to hear the seat heater switch assembly make a kind if click or "ching!" nose when you switch it; that's a relay energizing. It may do it at each switch position or at only one position, but if it does it at all, then the problem is most likely in the seat heater element wire itself. Although I have had a switch fail, seat heater problems are almost always in the seat heater element.
If you're at all mechanically inclined, you can do this. And it's worth it - the heated seats are WONDERFUL!

You can work on the seats while they're in the car (which saves having to remove the plastic trim panel and the seat belt anchor), or you can remove the seat completely to a place where you can work on it comfortably and with plenty of room. I've done it both ways; in either case, it's necessary that you completely unbolt the seats from the floor and disconnect the electrical harnesses. The last time I did seat work, on the Aero, I just turned the seats 90 degrees so they faced out the door of the car; this was a pretty reasonable working environment. Items highlighted in yellow are the minimum requirements - do only these steps if you want to just rotate the seats 90 degrees and not completely remove them from the car. If you want to remove the seat and take it to a work area, do the steps in white text as well.

Remove the seat (this is for power seats) -

Remove the T10 screw that's just below the center of the main seat control switch handle
Working from the rear floorboard area, remove the T10 screw that secures the outer plastic trim piece to the rear of the seat (this screw faces rearward)
Run the seat all the way forward
Run the seat as high as it will go, front and back
Pry out the circular plastic piece (from the top rear of the outer plastic trim piece) , then remove the T20 screw
Pry the handles off the seat control switches, then remove the plastic trim piece
Disconnect the electrical connector from the trim panel
There is a plastic side plate that blocks access to the seatbelt bolt - slide the plate forward to gain access to the bolt
the plastic plate will slide forward only when the seat is adjusted to it's highest position
Use a T40 Torx tool or a 17mm socket or wrench to remove the bolt that secures the seatbelt to the seat
Be careful if you use a 17mm socket or wrench, as the bolt head is not very thick, which makes it hard to grip
Remove the two seat-to-floorboard bolts at the rear Picture
A 3/8" breaker bar will help to release the (Lock Tight-treated) bolts
A breaker bar is stronger than a ratchet
It is also compact and will fit where a ratchet won't
Re-install the seat switch handle and run the seat all the way back
Remove the two front seat-to-floorboard bolts Picture
Tilt the seat back and disconnect the two wiring harnesses at the front.
Using an ohm meter, measure resistance from the yellow wire to the black wire on the larger plug (on the wiring harness that goes to the seat)
If more than a couple of ohms, the heater wire is broken, so proceed
(the resistance between the black and blue wires should be around 1000 ohms)
(this is the thermister connection)
Tilt the seat back, then sideways, then wrestle the seat out of the car, throw it over your shoulder and take it to your work area
The seat weighs 50 pounds and, due to its bulk, is more difficult to carry than a child of comparable weight
Assuming that the child isn't struggling
Which is a stupid assumption, isn't it?!

Remove the seat cover -
NOTE: when you first remove the seat cover, note the exact location of the thermister (it's the thing that senses the seat temperature). Take a picture of its location, or mark the location with a magic marker. If you fail to get it back in the right position, it won't sense the seat temperature correctly. This can result in the seat heater wire burning in two, or burning so thoroughly that it cannot be repaired.

All the following steps are necessary:

Two loops of stiff, heavy wire secure the front of the seat cover to a small diameter bar at the front of the seat. Use pliers to bend the ends so these can be removed. Picture Throw them away and replace them later with cable ties.

There was a cable tie on the inner side toward the front on my 94 Aero; this tie wasn't on the 91.

The seat cover is held in place by wire hook loops. They loop over a piece of stiff wire running around the inner periphery of the seat cover (the central U-shaped section, where your butt contacts the seat), then pull down and hook over the thinner wires that run across the bottom frame of the seat. There's one at the front of the U curvature (not on the Aero seats, I think), one on each side toward the front, one on each side midway back and one at each side toward the back. Look for silver wire pieces looping over the black cross wires. Picture

There are two ways to detach the hook loop wires:
Bend a 1/2" loop in the end of a coat hanger and slip the loop around the silver wire loop, then pull hard on the coat hanger and push up on the cross wire (use a stick to push the cross wire if it's hard to get to)
Be sure that your coat hanger loop doesn't grab the cross wire
You'll see the head of the hanger wire hook as you pull it down; twist the coat hanger and slip the hook off the black restraining cross-wire Picture

Another way is to grab the end of the hook-wire with pliers, then pull down and twist to disengage
Takes a good, strong grip

Try removing the front 2 or 3 hook loops, then lift the front of the seat cover and see if you can see a burned place that indicates the problem area. If so, you probably won't have to remove the rest of the seat cover . Picture
To completely remove the cover, remove the remaining hooks/hangers, then tilt the seat forward and remove the two similar wire clips that hold the back flap to the under-wiring

You can cut these if you want, and replace them with cable ties
Slip the front of the cover up off the seat bottom, then tilt it up. The outer wire frame of the cover hooks into clips at the back of the metal seat frame; tilt the cover up and slide it forward to release it
On the 94 Aero there is a seat controller module that gets in the way of at least one of the hooks. It's easy enough to swing it down out of the way. Picture

Find and correct the problem -

Hey, you think THAT was fun?! Now you have to find the break in the circuit! Ari has the tip of tips:

LOOK FOR BURNED SPOTS in the fabric that encapsulates the heater element wire.

If you're lucky, one of these telltale signs will show you exactly where the break is

Here's a close-up of the damaged area on my 94 Aero Picture

To get at the connections or the heater element wiring, you will have to cut the encapsulating fabric with a utility knife, then pull the fabric aside. The Aero heater element was buried more deeply than that on the 91. Using an ohm meter, monitor the connection points to the heater wiring (one black wire, one yellow wire); when the circuit is good, it should only read a couple of ohms.

Check the connections where the yellow and black wires connect to the thin black heater element wiring
If the location of the break isn't obvious, you will have to probe the heater wire at various points to see where continuity is and isn't. I scraped the insulation back at various points using the utility knife, and checked back to one or the other connector points (black or blue wire at the connector) until I was able to isolate the break. I covered the scraped spots with hot melt glue to protect them from further damage. If you can think of a better way to do it, please let me know. Frankly, I think it's risky to scrape the insulation back like this, but it's all I can think of to do when there's no obvious burned spot to indicate a break.

Suspect points where the heater wire crosses from the inner part of the seat (the buttock area) to the outer part (the leg support area). A pull test at these points might identify a break
Ari says that ALL of the breaks he has ever seen have been on the front outer edge of the seat (where the most wear occurs from getting in and out of the car)
Once you find the break, solder it back together and cover the repair with electrical tape, or put a piece of heat shrink sleeving on before the repair and shrink it down afterward. Ari likes the heat shrink method. While it's tough, I worry about its flexibility. I also cover the repair with a couple of squares of duct tape to help protect it. Don't get carried away with tape, as it won't conduct heat.
Connect the wiring harnesses, start the engine, turn the seat heater on and sit on the seat a few minutes to see if it heats up. Use common sense about exhaust fumes; as in, don't sit in the idling car with the hatch door open, or in a garage, or in any situation where exhaust fumes could collect.
According to the Haynes manual, it's not a good idea to let the car sit with the ignition switch in the run position but without the engine running.
Be advised that seat heat will be subtle, particularly when it's not cold outside, and it may not come on at all when it's warm out.

Re-assemble the seat -

Tack the heating element and fabric down with hot melt glue wherever necessary
Try to get the thermsiter back exactly where it was originally; it monitors the heat and sends control signals back to the switch/controller
If you don't know where it was, position it near a heater element loop
Slip the rear seat cover flap under the seat back/bottom joint, tilt the front of the cover up and fit the ends of the cover wire into the tabs in the frame at the rear, then fit the cover to the seat
If you forget to secure the ends of the wire into the clips, or if they slip out, you can bend the clip tang out slightly so the wire rod can be slipped into position
You can re-use the wire hook loops, or you might try long cable ties. Picture Cable ties work OK on the front and back positions, but it's too hard to get to the two middle positions. All in all, the hanger/hooks work pretty well and aren't too hard to deal with once you get used to them.
Start at the rear and furthest from you
Put the hanger wire/tie onto the wire frame on the cover
Hanger: Hook the bottom part with your coat hanger hook
Pull the hanger/tie down through the opening in the seat foam
Push up on the cross wire, pull the hook from the bottom and
Hanger: Hook the hanger onto a black cross wire
Cable tie: Secure the tie around a cross wire, cinch it up and clip off the excess
Repeat for each, working toward yourself, then toward the front
Use cable ties to fasten the front seat cover wire to the subframe wire
Use the hanger clips or cable ties to fasten the rear flap to the subframe wire

Re-mount the seat -
Leave the plastic side trim piece off until the seatbelt anchor has been re-installed
Connect the wiring harnesses to the floorboard connections
Align the front mount holes, install the bolts and tighten them finger tight
Re-attach the seat belt anchor to the seat
Re-install the plastic side piece (the top lip slips under the side of the seat cover and wire rod)
Install the screw under the switch and the one at the top rear side
Re-install the plastic plug and the switch handles
Install the screw that secures the trim piece to the rear of the seat
Run the seat all the way forward and install the rear bolts. Tighten them firmly but don't over-tighten them and snap them off
Run the seat back again and tighten the front mount bolts
Check seat positioning and heater operation
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