As the seat back comes off, maneuver the green and blue electrical connectors out of the seat bottom. They’ll remain with the seat back.

Remove the seat belt connector. T45 again.

Seat bottom cover is held down to seat frame on all 4 sides by different types of fasteners. Hog rings, J hook tabs and a white clip. You’ve already removed the hog rings on the rear gray fabric tab. At the front of the seat, there’s another gray fabric tab which may, or may not, be held on with hog rings.

This front gray fabric is a little different though. It terminates in a gray plastic J hook that snaps over the thick metal wire. J hook is just like it sounds. Plastic tab is a hook, shaped like a J, when viewed from the side. The shorter side of the J is closest to the seat foam. Remove any hog rings, pry the J hook off the wire.

The inboard side of the seat has the same hog ring/J hook configuration.

Finally, the outboard side of the seat has a white plastic clip, with tabs that go through seat frame, which need to be carefully pried out. White clip is sewn onto the seat cover and will be re-used.

Slide the seat adjustment wiring out through the cover. Once all four sides of seat cover are free from the metal frame, remove the seat bottom from the frame. Thick foam cushion and cover will come off together.

There’s a black tab holding the cover to the foam cushion. Slide it sideways, then tuck it down into the foam.

Then you can begin to remove the cover from the seat bottom foam cushion. Carefully. There’s Velcro holding the seat bottom cover to the seat cushion along the bolsters. White pile on the seat cover and blue hook & loop on the seat cushion foam.

It’s easy to accidentally tear the blue Velcro away from the seat cushion foam. It’s also fairly easy to repair with contact cement, but save yourself my trouble.

 

Now you’ll be left with just the leather cover and it’s sewn-in foam and wiring.

There are four sections to the seat bottom cover. Each section has a heating element in it. For the sake of clarity, refer to below diagram.

Left Outer Element
Left Inner Element (this area also contains the thermistor)
Right Inner Element
Right Outer Element

Individual Seat Element Testing:

Before you disconnect those green connectors, I’d label each one so you know how to put it back together correctly. All 3 green connectors are identical and it can be put back together “wrong”. Ask me how I know. I labeled them Left, Middle and Right plugs. Once the 3 are disconnected, check each element as follows:

Left Outer: Check for continuity/resistance at the Left Green Small Male plug. Two brown wires.

Left Inner: Check for continuity/resistance between the Left Green Larger Female plug (green wire) and the Middle Green Female plug (blue wire).

You’d think the next one would be Right Inner Element, if we were going in L to R order. But that’s not the order the elements are in series. Current actually flows L Outer, L Inner, R Outer, then finally to R Inner. Go figure.

Right Outer: Check for continuity/resistance at the Right Green Small Male plug. Two brown wires.

Right Inner: Check for continuity/resistance between Right Green Larger Female plug (green wire) and Middle Green Small Male plug (blue wire).

Now you should know what zone your wire break(s) are in. Time to open it up and find them. In the event you have an open thermistor circuit (no resistance/no continuity), the same ‘tear it open’ applies here too. You’ll just be opening up the foam where the Left Inner Element is because the thermistor is located there. Thermistor itself (the “watch battery”) is located under that small square of white fabric.

Blue wire is the heating element. They’re snaked back and forth along the whole area of, in this pic, the Left Inner Element. I’ve read other forum threads where the heating element wires were a different color and/or uninsulated. Your mileage may vary. Gray wires go to/from the thermistor. I found the thermistor was placed directly on top of the blue wire. I would imagine to get the most accurate reading of the temp the wire itself was generating.

Initially, I had a broken wire to my thermistor

The TSB says to “carefully slit the foam using a sharp knife”. Meh. I’ll agree with the carefully part. Reason being all the seat heat/thermistor wires between the foam and leather. Started with a sharp knife and just ending up tearing by hand. Think it actually helped when it came time to glue the foam back together since the edges were jagged and there was only one way to put the two jigsaw puzzle pieces of foam back together.

Pic of Right Inner Element wiring. Note the lack of thermistor wires here.

This is the hard part, maybe. Actually finding the break in your heating element wire. Most of the time, the break is right after the larger gauge wires enter the foam. IOW, where they are soldered to the thin blue heating wire. This is exactly what the TSB addresses. I had one break here on the Left Outer Element. Makes sense, right? That Left Outer Element is what we all put our weight on as we slide into the seat every time.

The Right Outer Seat Bottom Element was fine.

But continuity checks told me I still had a heating wire element break in the Left Inner. Had to open that zone up like an open heart surgery patient, checking for wire breaks the whole way. Murphy was working overtime that day because my break was here, all the way at the front of the seat cover.

At least, when I found it, it was pretty clear where the broken wire was. Burn mark and everything. I would imagine it’s possible to have a wire break, still contained within the blue insulation, that you’d never see. Which would really up the hassle factor in finding it.

 

The blue heating wire is quite thin with some surprisingly tough insulation around it. Initially tried a razor blade to strip it, but the silver wires inside cut too easily. The 28 awg hole in my wire strippers worked way better! Soldered the heating wire break and put a little heat shrink around it. Mostly for strength, not so much for electrical insulation because, after all, the wire is designed to heat up.

Used hot glue to tack the wires back in place. It appears they used something very similar at the factory. Learned a little something about hot glue in the process. There’s more than one type, “multi-temp” and “hi-temp”. Interweb yielded varying answers on exactly what temp these two kinds will melt, so I can’t say for sure, but it was clear that hi-temp stays solid at a higher temp than multi. I just wanted to ensure that routine use of the heat wouldn’t weaken my hot glue, so I opted for the hi-temp glue sticks.

Used contact cement to glue the foam back together. Was also going to put a duct tape ‘band-aid’ over the foam ‘scar’ when finished. But I found that the contact cement, when fully dried, held the foam together quite strongly.

Recommendation: As you put the seat back together. Keep checking the heating elements and thermistor readings along the way. Nothing worse than “fixing it”, only to pop it in the Jeep and find that you’ve induced another wire break along the way.

Another odd thing I encountered that you may too. Learned the hard way to pre-position the seat recline so the aft seat back bolt is exposed BEFORE you remove the seat from Jeep power. I briefed that earlier in this thread. But at the time, I thought, no big deal, I’ll just apply 12V power directly to the connector when it’s on the bench.

And that worked. Just fine….for the passenger seat. Oddly, it did not work for the driver’s seat. Thought maybe I had broken something in the whole tear down process. Once the seat was connected back up to C329 (driver’s seat power umbilical) all the seat motors worked perfect. A very smart friend of mine hypothesized that it may have something to do with the fact that ONLY the driver’s side has the seat posn/mirror memory module and that module (located under the seat) needs input from the CCD bus. Driver’s seat connector C329. Note the 6 wires, D1 and D2 are the CCD bus inputs:

Passenger seat connector C335. Only 4 wires, no CCD bus connection:

In both connectors above, pin Z1, 16 gauge black wire, is the ground wire. When the seat is out of the Jeep, it’s probably a good idea to test that you have a good ground at each front seat connector. I had a wonky ground on the driver’s side, that gave me fits chasing down. It showed good continuity (less than 2 ohms resistance) with Key Off, Key Acc, and Ign On. But when I started the Jeep, continuity went away. Ohms jumped up to 120! According to the FSM electrical diagram, the driver’s side is supposed to be grounded at G302/G303. Both grounds are on a metal hump underneath the carpet, driver’s seat side.

G302 and G303 are there where they’re supposed to be. But, spoiler alert, the driver’s seat is not grounded there. I pulled my carpet, checked both grounds, removed, cleaned, shined up to bare metal and retried. Same result.

Unfortunately, I’m the type that’s tenacious to the point of stupidly wasting my own time. I had to win on this. So out came the carpet (great time to clean it, I rationalized). And it does actually clean up amazing when you pressure wash it! Just takes a couple days to fully dry.

Side trim over front seat belt and both door jambs came out. All to get access to giant wire bundle going from front to rear

Unwrap the wire bundle (great time to add Dynamat to the floor, I rationalized) and trace out that Z1 ground wire for driver’s connector C329.

Like I said, the ground is supposed to terminate at G302/G303 there under the driver’s front seat. It does not. That Z1 ground wire travels aft along the driver’s and pax door jambs. There’s two grnd splices that peel off and travel up the B pillar. As it makes a turn toward the pax side, another splice peels off and continues aft to the left rear wheel well area. Bundle turns the corner, travels under the rear seat, behind the power amp, and over to the pax side.

Right between the power amp and the g-switch (on center hump under rear seat) there’s the Mother Of All Splices where 6 ground wires are crimped into one larger 12 ga ground wire that continues over to the pax side. Eventually making its way to ground point G301 on the metal hump under the pax seat. What this means is the driver’s seat power was actually grounded underneath the passenger seat.

 

Coincidentally, or not, the fuel pump ground wire is one of these 6 wires shown. That fp grnd wire goes straight aft from the 6-1 splice thru the frame to the fuel pump. Full credit for figuring this out goes to forum member RDC_ZJ. I was stumped. My wonky ground was only happening with the engine running. Upon closer inspection, it was also happening when I turned the key to Ign On. But just for a second. The driver’s Z1 ground would jump up to 120 ohms and 2 secs later go back to good continuity/essentially zero ohms. And as reported earlier, when engine was started and running, the ground resistance would jump up to 120 ohms and stay there. Well what do those two ignition positions have in common with the fuel pump? Hmmm. Somehow, and I’ve no idea how, the operation of the fuel pump was robbing me of my Seat Heat ground. The splice itself actually looked ok, but I redid that crappy 6-1 splice anyway. Ran a 10ga marine wire from G301 under pax seat, all the way back to the 6-1 ground point. Barrel crimped and heat shrink. Also took the Z1 wire from C329 and grounded it directly to the metal hump under the driver’s seat. Where it’s supposed to be. Ran a new ground wire from C335 directly to metal hump under the pax seat. Repeated my ground tests. All fixed.

I want to add a shout out to RDC_ZJ, who helped me greatly with this project. Not only with my understanding of it all, but in the actual fine wire repair too. Just for fun, he re-engineered a Heated Seat Switch Pod to show Red LED backlighting on High and Green on Low! He has also worked up electrical diagrams of the HSCM (Left AND RHD!) and the Heated Seat Switch Pod. Guy knows his stuff. Hopefully, he can add those schematics to this thread so all the info is in one place. Thanks again, RDC!

As always, if I got something wrong, please add a correction. Hope this helps some of you get those inop heated seats back in working order, or at least saves you the ‘learning process’ time that, for me anyway, always seems to eat up so much time.

 

dam samuel
should be a stickie

 

Great write-up

Passenger seat heater works in my first ZJ, driver's side wasn't working when I bought it in 2010. I pulled the seat and got lucky years ago, the cut in the heater wire was at a solder point located in an easy-to-access area. Heater stopped working again a couple years later, after which I haven't done anything to it. Non- heated leather seat when it's -10...-15°F isn't fun, but I guess my butt has gotten used to it during my 42 years in cold climate and working outside for the past 21 years.

The second 5.9 I bought before x-mas has the same issue on the drivers' seat, not sure if I'm gonna do anything about it or not. This ZJ has a bunch of other things I need to do (HVAC system is INOP, most likely wire related, sunroof won't close although relays click, and a few other small electrical gremlins), so when fixing those I might follow this write-up. I'm just not too keen on diving into the seats, I'm afraid on tearing things up.

 

Switch pod and HSCM schematics. The LHD and RHD HSCM essentially do the same thing, but they are not interchangeable as they use different connectors.

Possible Thermistor replacement. Who knows what the actual specs on the original are anymore, but this one should get things going again if you have a bad or damaged one in there. - Part # RL3006-5340-140-D1 and it can be found at DigiKey, Mouser and the like.

 

Fantastic write up!

 

Does anyone have an exact ID and source for the blue resistance wire? It's time to rewire the seat bottoms with all new blue resistance wire.

I suspect it is some Nichrome alloy stranded wire insulated with a Teflon jacket. Over the years I installed several Mopar seat heat repair kits, P/N 05015478AA, but thousand mount/dismount cycles of the driver seat and to a lesser extent the passenger seat have created many fatigue breaks in these blue wires.

 

it fixed, always nice to have toasty buns when it’s cold out. Lol


192.168.100.1 192.168.1.1

 

Update: Just learned this today. Evidently there are two different HSCMs. In 1996, the first year of ZJ heated seats, the HSCM is part #56042055 Revision A. In 97 & 98 it’s part #56042055AB. Same location, same function, however, different shape module and different wire pigtail. The Rev A wire pigtail also has a release tab you have to depress to release the module unlike the 97/98 which just pulls straight out of its pigtail like a typical relay.

So for those of you troubleshooting a 96, when you do the continuity checks described above, the A-F check and the E-F check, use this conversion chart graciously supplied by forum member RDC_ZJ. This applies to Rev A modules and also RHD ZJs.

A=3
B=NC (no connection)
C=1
D=2
E=8
F=7
G=NC
H=NC

IOW, your A-F heating element continuity check would be between pins 3-7 on a 96 or a RHD. Your E-F thermistor check would be pins 8-7.

 

Sorry for resurrecting an old thread. But what do we do when the seats get WAY too hot?
My drivers seat on my 98 ZJ gets unbearably hot that I have to lean forward until it cools down, however the passenger seat gets comfortably warm, way less warm than my drivers seat

 

My drivers seat on my 98 ZJ gets unbearably hot that I have to lean forward until it cools down

Is that on just Low or is it the High setting?

sounds like the thermistor: 1. may not be close enough to the heating wire, and/or 2. may need to be replaced.

As a quick and inexpensive troubleshoot, swap the HSCM’s and see if it behaves the same. If it does, then the problem lies downstream of those.

OR, bring that seat on over and I’ll trade driver’s seats with you 😉. Its 27 outside, snowing and i have to drive to work right now.

 

Read the write up. It explains the system in detail.

 

Probably has nothing to do with the fact the driver seat was cut in the middle from front to back and the thick black wire between the cushion foam have been wrapped together in electrical tape? Surely not :^]