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PostPosted: Tue Feb 16, 2016 12:39 pm 
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Resident Gearhead
Resident Gearhead
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Joined: Mon May 19, 2008 10:30 pm
Posts: 8685
Location: Grand Rapids, Michigan
Year and Trim: 2014 Cadillac XTS Vsport.
Author - ddalder


Rear Outboard Heated Seats Project

This is very long so grab a coffee...

For about the last year I’ve been working on my rear heated seats. I have a personal policy of not adding or changing anything that I can’t make to look and work like a “factory installed” option.

My biggest hurdle was the switches. I wanted something with an OEM look that could be mounted in a place GM might use. For me, this was in the rear door panel. There isn’t enough clearance to use the “Bonneville” switches so these weren’t an option. I looked at several others but finally settled on some from the ’97-’99 Park Avenue. They have a black face (to match my others), they are a GM part (mandatory), they have a small enough profile and the font is close to, if not the same as the other Bonneville switches.

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Next was the problem of a switch bezel. I lost count of how many cars I went through at the wrecker looking for possibilities, or at least one that I could make work for this application. Long story short, I ended up using power door lock bezels from an early 90’s Saturn. These are obviously not ideal in their “raw” state so off to work I went. Here’s the original donor switch.

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I successfully created a “test” bezel to ensure these would work. For the final product, I had a plastics shop professionally enlarge the opening to fit the new switches.

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They still didn’t look great so I smoothed and reshaped them for a more “correct” appearance. I used a variety of sandpaper grits until the final step of wet sanding.

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To make the retainers, I had to modify the existing spring steel clips. I had to heat them to make the sharp bend without breaking. A torch and Dremel were invaluable.

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Now with a switch and bezel, there is the issue of backlighting. The Park Avenue lights up green, not a good match for the Bonneville. The backlighting is poorly designed and doesn’t lend well to a crisp appearance. It’s not very bright and in my opinion, completely unsatisfactory.

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Here’s the inside of the switch. I removed the incandescent bulb and replaced it with a custom sub-assembly using LED’s. I had to add a current limiting resistor in-line with this. I cut a trace on the printed circuit board to facilitate the resistor. I pre-shaped the leads and insulated it before installation. I exposed a small amount of copper from the printed circuit board trace to connect one lead of the resistor. The other lead was soldered right at the connector pin.

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I used one LED to illuminate the “HEATED SEAT” text and another for the symbol. Many LED’s have a narrow beam angle so I reshaped the lenses for a wider, more even spread of light. You’ll see in the picture of the LED sub-assembly, the larger and brighter LED is aimed just above the top of the mechanical switch and not towards the front of the switch housing. I used the clear plastic post that is part of the pushbutton as a “light pipe”. It carries much of the light from the LED to the face of the pushbutton. This scheme has been used in automotive backlighting for years. Some reshaping deflects light forward, but also ensures everything will fit in the housing.

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And the finished switch...

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After the switches and bezels, the rest seems straight forward...

In the spirit of “OEM”inism, I created wiring consistent with what GM would have done. I added wiring to existing sections of harness (doors and door panel harnesses) or built new, custom sub-harnesses. I used all new wire and OEM terminals. There are no splices and all terminals clip into factory connectors. Here you’ll see what I did with the door wiring. The trim panels only have a 10 cavity connector. After the adding courtesy lights, I didn’t have enough capacity for the five switch conductors. I changed these to 18 cavity Lever Lock connectors like those used on the front door panels. Of course I used actual wire harness tape throughout.

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The majority of new wiring was in the addition of the control modules. I wanted to make it easy to remove and install the seat cushion and seat back. I mounted the control modules on the rear of the seat back and built a custom harness that terminated with a 22 cavity Lever Lock connector.

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The other half of the Lever Lock connector mounts on the left diagonal cross brace behind the rear seat. This is wired to another custom harness routed to the fuse block, ground, door panel switches and the seat cushion integrating all required components.

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I modified the rear fuse block and added separate fuses for the left and right seat circuits. This was done in the same manner as GM used in other vehicles with this option. The grounds were tied into the factory splice pack underneath the rear seat cushion (left side). The backlighting connects into the splice pack under the driver seat.

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The next step was the heating elements. Because the control modules interchange between the 2000 LeSabre (donor vehicle) and the Bonneville, I used the GM seat element service kit made for the Bonneville GXP. This ensures the elements are a match to the modules. The modules will have been designed for elements of a specific resistance. It’s important that the thermistor (located in one element pads) is correct for proper temperature sensing and regulation. With an element/module match, there is less chance for fire and other problems. Yes, the element kits are quite expensive!

Some element pads are too large and I had to do a little trimming. By holding the elements up to the light, it’s possible to see where safe cuts can be made. I made sure I didn’t trim too much and left a safe margin between the element wire and the edge of the pad. The elements have an adhesive backing and are applied to the foam of the seat assembly. I technically installed the seat cushion elements “backwards”. The wiring is more toward the front of the seat. I’m hoping this will prevent the same failure seen in the front seats by keeping the weight of the buttocks off the wiring connections of the element pad. This doesn’t change the coverage area of the element at all.

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To remove and replace the seat covers properly you will need a pair of hogring pliers and some hogrings. Hogrings are the small metal rings that hold the upholstery to the seat frame. I was able to get the tool from a Mac dealer for about $30 CAN. Hogrings are available at the GM parts counter in bags of about 50. This is roughly the number I needed (although I bought mine elsewhere). At the time, I didn’t realize I could purchase small quantities from dealership.

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By NOT completely removing the seat covers, it helped to ensure they were well aligned for reinstallation.

Since the elements are made for the front seats, and the front seat cushion and seat back are not intended to be taken out separately, the wiring was not configured for an ideal rear seat application. I modified the element wiring (at the connectors) in such a way that I have a single connector to disconnect the entire seat cushion from the vehicle. Electrically they are identical to their original form. All five element segments in each seat position (for the GXP style seat, three in other kits) are wired in series.

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So I’m pretty much done... right?

WRONG! I still have to mount the switches. I have the switch and a bezel but in the current form will not look factory. The trim around the door handle has a carbon fibre appearance, but the new switch bezel is unfinished plastic. Because these will be beside each other, it’s a bit of an appearance nightmare! I decided to try and have the new bezels finished the same as the other “carbon fibre” trim. There are a few companies that do hydro graphics printing and are technically capable. The problem is no one could match the GM pattern. I contacted Frank at Custom Hydro Graphics in Texas who was able to help with an alternate solution. He was fantastic to deal with. I sent ALL my existing carbon fibre trim pieces to him, along with the new seat switch bezels. He refinished everything in an available carbon fibre pattern. Not only does everything match, it looks far better than the original!

The first picture shows the factory GM pattern. As you can see from subsequent photos, the original is very “brown”. The new finish, from a colour and pattern standpoint, looks stunning with my gray interior. In all I sent my steering wheel, all four dash vent pieces, all four door handle trim pieces, the vent from the rear of the centre console and three new heated seat switch bezels (one spare) to be processed.

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And of course the cause of this all... the new switch bezel!

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I’m in the home stretch! All I had left was to cut holes in my door panels and mount the switches. This was a little stressful to say the least. There aren’t many GXP’s in the wreckers and so if I messed this up, getting replacement panels could be difficult and expensive. Buying from GM would have cost about $600.00 each. To improve my chance of success I bought a door panel off a 2000 SE to use as a test. I learned a lot from this and believe it was worth the expense.

I made a transparent template using some landmarks on the door panel. This allowed me use it on the left and right doors. It made easy work of placing the switch in the same spot on both sides by simply flipping it over. I’m not going to get into too much detail here. I will say that there’s little margin for error and patience is crucial. The opening was cut using my Dremel and a file.

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Here is the finished product!

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This project cost a lot more than I first anticipated.... A LOT MORE. Probably best not to ask!

_________________
*Gone, but not forgotten* - Black 2000 SSEi, HIR Headlights, Angel Eyes fogs, 3rd brake light overlay, hi-flo cat, 180 degree thermostat, HS 1.9 rockers, LSx yellow springs, Intense FWI, PCM, shift kit, push rods, and 3.4 Pulley. ZZP Power Log.


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