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How to Guide: Install heated seats using the OEM heated seat switch


j_jza80
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After getting mine to work at long last, I thought I'd post up a guide so that no one else had to suffer as I did! :D

 

First of all, a big thanks to Scott and Sketch. Their help in THIS thread was invaluable.

 

Next, just to cover myself, I am not an auto electrician (hence the basic diagrams you see here). I fitted car electronics for Halfords while I was at Uni, and have literally fitted hundreds of car stereos, hands free kits, accessories etc, and have done countless bits on my own cars. Even so, this is only presented as a guide, you are responsible for any work you do on your own car, and always seek the help of a professional if you are unsure of something. Now that's out of the way...

 

What you'll need:

 

- OEM Supra heated seat switch. These can be found used, as all UK specs had them, as did GZ TT's. Still available new, but over £100 at the time of writing. I'v been paying circa £15 for used switches

- Heated seat kit. various types available, but a basic one will be fine. Carbon panel ones are slimmer and easier to fit, the cable type tend to be tougher and warmer. I used THIS

- 2x 30a 12v on/off automotive relays. The heated seat kits tend to come with one.

- female spade crimp connectors for the relays

- male and female bullet connectors

- Ring connectors for grounds

- cable ties

- insulation tape

- Wiring - match or exceed the size your heated seat kit comes with.

 

For the connections into the switch, you can buy the factory connector and leads from Toyota. You will need:

1 x 90980-10933 "HOUSING, CONNECTOR 6 PIN" (connector)

6 x 82998-12440 "TERMINAL, FEMALE" (leads with female ends that push in to the connector)

 

Or, you can just do it with female spade fittings and save yourself £40, though you will need to mark them so that you will know what goes where in future!!

 

I would highly recommend initially installing the kit using bullet connectors to start with, and once you know it is all connected properly, soldering and heat shrinking the connections for a permanent, reliable system!

 

 

 

1. Fitting the seat heaters

 

This will vary from seat to seat, and the kit you use. But basically you need to remove both of the front seats from the car, and remove the covers. Go carefully, make sure all wiring is disconnected from the seats, and watch you don't catch any of the interior trim when removing the seats! The doorcards especially are very easy to mark.

 

Removing the seat covers isn't usually difficult, but it is slow, methodical work to do without damaging anything. They are usually held on with a combination of zips, staples, metal rings, and plastic 'push fit clips'. You may also need to remove plastic trim pieces, depending on the seat design.

 

Once the covers are off, you need to place the elements (one for the bottoms, one for the backs on each seat) on the foams, and fix them down using the self adhesive tape supplied. Carefully feed the wiring through to the bottom/back of the seat, near the tilt hinges, but use cable ties to ensure the wires cannot get caught up. Some insulation tape in vulnerable looking areas won't do any harm! :)

 

Now refit the covers. It is probably worth connecting the elements up to a 12v source at this point to test them before doing so, because you won't be a happy bunny if you have to strip the seat down again! :D Don't refit the seats yet, because we still have wires we need to feed through!

 

 

2. Modifying the heated seat kit wiring

 

Most of these heated seat kits come with 3 position switches ('off', 'Low' and 'High'), which we will be removing in favour of the stock switch. The stock button only has 2 positions ('On' or 'Off'), so we'll need to decide how to wire them. In my kit, the switch was like this:

image

 

The centre wire is the permanent 12v in, the top wire the 'high' circuit wire, and the bottom one the 'low' circuit wire. So connect the middle wire to either the top or the bottom wire, and insulate the spare other. I wired them all together, which works with mine, but I wouldn't recommend it unless you test yours thoroughly like I have. And it gets VERY hot :D The switch may also have an earth connection, so just unplug that and then remove the switch from the system.

 

Now we need to modify the the seat heaters single relay setup, to use two relays (one for each button on the Toyota seat heater button). This is how the seat heaters came wired in my kit:

image

 

To make it work with the stock switch, we need to switch from a single relay, to two. One for each seat, operated by the corresponding button on the Toyota heated seat switch. You cannot wire directly through the switch without relays! The switch will burn out. So this is how you wire it for two relays:

image

 

 

3. Installing the wiring

 

To start with, you really need to remove the dash panels, and preferably the radio. Have the heated seat switch handy, don't fit it to the panel yet.

 

Permanent live: This needs to come directly from the battery, or preferably from the 'live bolt' in the enginebay fuse box if you don't like lots of things cluttering up your battery terminals! :) Wrap the wire in black tape to keep things subtle in the engine bay, run it behind existing wires and pices, and secure often with small cable ties. I find the best place to feed it through the firewall is through the large grommet near the steering rack, which comes through behind the dials. Seal the grommet up when finished.

 

Ignition live: This can come from the cigarette lighter, or even the stereo.

 

Ground/Earths: should be as short as possible while allowing things to be moved or removed. Plenty of available bolts in the trans tunnel area behind the dash. Use a secure ring terminal.

 

Illumination positive and negative: can come from the light on the back of the cigarette lighter, or the clock. You must use the ground circuit if you wish the seat lights to dim with the rest of the dash lights. Don't mix these up or you will fry your dash dimmer switch! (as I found to my dismay :D ) The negative illumination wire on the Supra loom is White/Green.

 

The relays can be located in the vast area behind the stereo. Once all the wires are connected, route the wires that will connect to the seats along each side of the firewall behind the carpet, and then under the carpet where the seats are. Make sure there is enough play on the wires so that the seats can be moved within their full range! If there isn't already a hole in the passenger side carpet, carefully make one, and make sure it is hidden!!!

 

Make sure all the connections are made on the back of the switch, and that they are secure. If you are not going to buy the oem Toyota wiring block, I recommend you use well fitting female spade connectors (close them up a little with pliers if you need to) and one firmly in place, secure to the back of the switch using insulation and preferably some stronger ducktape too. Fit some male and female bullet connectors to the wires maybe 5-10cm behind the switch, and make sure all the wires are labelled up for future reference!

 

 

 

4. Finishing up

 

Once all the wires are in place, refit the seats without securing them down, and plug in the seats to the wires you just pushed through the carpet. Put the key in, turn it to the accessory position, and press the seat heater buttons. It may take 20 seconds or so for you to start feeling the heat coming through, an maybe a couple of minutes for the full effect to be felt. If you have done everything properly, you now have awesome heated seats!! :dance: If they aren't working, retrace your steps, methodically eliminate potential causes.

 

Once you are sure it is working and you are happy with it, you can start refitting everything. Secure the carpet, bolt the seats down, refit the stereo, fit the heated seat switch to dash panel, and replace all panels (making sure that all the wiring connectors are put back - if something isn't working later it's probably because you forgot something!)

 

Once you're done, you should have something like this:

image

 

image

 

And a warm bum! :D Now you can use your pride and joy during winter.

 

Also, there's no reason why you couldn't repurpose the switch for something else. You could modify it to run an auxiliary fan, engine bay lighting, security, exhaust cut off valve etc.

Edited by j_jza80 (see edit history)
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Awesome, I wanted to use the oem switches when I did mine but didn't work out. Does your allow you to have 5 different settings? as I went with this one

 

No, the factory switches are only ON and OFF :) The thing is, your switch fits in with your modified dash, but wouldn't look nice on an otherwise stock-ish looking dash. You could run it through the switch the seat heaters came with, which would give you adjustment and use the OEM switch, but it's just another thing to hide away somewhere.

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Good guide that J. Should request a move to tech so that it doesn't get lost in the chat of doom :)

 

I'm using the heated seat switch body with a couple of alterations in order to use it for line lock and rear fog lights. Heckler was on hand to sort me out as ever though :D

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Mate as I said last night I'm gonna be doing this today and the write up sounds 100%. I have been looking into this for the last 3-4 days and not really getting any really true ideas with any 100% answers

 

This really needs to be a sticky as like a couple of guys have said

 

Many thanks for top efforts taken to write this up and there own time to help all of us all out :thumbs: :thumbs:

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Great thread.

 

Im looking to fit my OEM switch into my oem uk heated seats, not sure if it woulld be the same wiring? Fancy having a go at doing mine ;)

 

The wiring diagram I've posted should work fine for yours :) there may be differences on the actual seat wiring, but I doubt it.

 

Good guide J! Moved to FAQ's and Guides

 

Cheers mate :)

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