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Solved Seat Heater (heated seats) installation using factory fuse and relay

Asmara

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There are several threads on installing seat heaters aka heated seats but the ones I have seen, have you tap into the fuse box. I like to keep my installs looking stock so I decided to pull the wiring diagram and trace the seat heater wiring to see what I could find.

It turned out that in my Tacoma ('21 SR5) it is pre-wired for seat heaters. A little more sleuthing and I found that the factory installed a seat heater fuse but no relay. With the relay installed, the factory wiring worked as expected i.e. the circuit was hot when the truck was running and turned off when the truck was off.

I took some pictures along the way that are attached. The switches look factory except for the fact that the blue light is always on (not controlled by the headlights) and the low/high indicators are orange instead of the green used everywhere else. I've already ordered some green LEDs and plan to change them out to make the switches look even more factory.

What you need to know:
The empty relay location is behind the switches to the left of the steering wheel. You can just reach up behind there and pop out the switch plate to see where the relays go. I bought a genuine 4 pin Denso relay (567-0001) from Amazon but there are tons of cheaper off brands as well. I couldn't find the part number for the factory relay but the 567-0001 supports 20amps which is what the fuse is so I don't anticipate any problems. When I bench tested the seat heaters it pulled about 4 amps a seat on high. Install this relay and the seat heater circuit will be live.

Next I located IE2 which is the junction for the seat heater going to the driver's seat. It is behind the driver's side kick panel. Per the factory diagram, the seat heater is on pin 5 of IE2. During testing, I determined it is actually on pin 4 of IE2. I cut the wire coming out of pin 4 and spliced in my seater heater wiring. I only needed one connection for both seats because I combined the two wiring harnesses behind the switches.

I knew I would need a ground point and, fortunately, there is one right next to IE2.

I wired everything together and the seat heaters work great.

I'd note that you could use this circuit to power any high current device you want (lighting for example) and just re-label the fuse panel. Also, when enabled you have +12v going to both seats so there might be something else you could do with that that might be useful.

I hope this helps some people. I know it will save some time on wiring up a seat heater install.

edit: added term heated seats to help with searching.
 

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Can't really tell anything from the photo but you would have a total of 3 relays. The two that are part of your Clazzio kit and one that is the OEM relay. @Athena32 posted above about a Clazzio install using this technique and may answer a PM.
 
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Thanks for the great post. Another 'add' is that i wired into the factory wire on the passanger side for the passanger seat. IL3 Pin 7 (was blue in my 2023 trd sport)


1674154243969.jpeg
 
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Awesome guide! I'm attempting to wire the Clazzio heated seats to my 21 TRD sport 4x4 currently and I have some questions:
A. Seems like the wire you tapped for power is actually used for the power seats in mine. I can't see that it will matter if I still tap into it (as long as a keep the power for the power seats). Does it? I prefer not to do it this way but I may have to.
B. My Clazzio kit has 4 wires total to hook up; (1) "Thick Red 12g - Constant (+)", (2) "Thin Red 16g - Switched (+)", (3) "Black Ground (-)", (4) "Yellow - Illumination". I think wire #2 goes to the switch to turn the seat heaters on and off? From the other comments in this tread, it seems like I can wire it to the same place I wire #1?
C. I plan on wiring this to something that only comes on when the car is on (not always on and not acc). Is this ok? Would it be ok to hook up wire 1, 2, and 4 to the same power source?
D. Since I don't really want to tap into the power seats, could I use a fuse tap and add a fuse to something like sunroof? (which mine doesn't have)
E. Does it matter that all the power wires I have found are 16g (including the fuse tap) but the power wire to the seat heaters are 12g?

Edit: I found some charts, it does seem like 12g would be correct here. Seems like there will be a max of ~10amps being pulled and probably over 6 feet in wiring. So the question is, where do I get a 12g wire from? Seems like all the wires in the truck are 16g. Should I run wire #1 directly to the battery and wire #2 to something that turns on when the car is on?
 
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A. Double check the wiring. I have a 2021 SR5 double cab. It it possible that the access cab (if that is what you have) is different. I might have that wiring diagram somewhere but I only saved the double cab diagrams when I accessed the TIS.
B. Yes, you can draw from the same source without a problem. It sounds like your harness uses a relay to switch the seats on and off. Mine ran all the power through the switch but there is nothing wrong with using the same power supply location.
c. Yes. This is ok but I would note that was the whole point of using the empty relay slot. That uses the factory seat heater fuse with the factory relay location. That relay is only energized when the ignition is on.
d. You can use any appropriate circuit. Power is power. The point of this was to keep everything wired as stock as possible (see c).
e. I tested everything on a bench and my seat heaters only pulled 4 amps on high for each seat or 8 amps total. Rule of thumb is 16 gauge can handle 10amp loads. Additionally, and I can't remember exactly where I saw/read this, you'll note that the Toyota seat heater wiring is only 16 gauge. They have it on a 20amp fuse. There was something somewhere about this in the Toyota documentation noting it was OK because the wire was different. If I recall correctly, the insulation was different when I stripped it.
 
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Great post. I have a 2020 sr5 double cab. I have the S/HTR fuse and it appears my relay slot is wired. I have the sky blue wire on the front of IE2 but NOT the back.

I'm thinking it is challenging to add a wire to the fuse box to IE2? Any suggestions for other switched sources for pulling power?
 
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That is the wire. That connector (with the sky blue wire) plugs into IE2. You would be hard-pressed to even see the back of IE2 although someone with an SR didn't have the wire in the front, it did exist in the back.
 
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For an update:

I ended up using the add a fuse ($10 for a pack of 10 from Amazon) to get power directly from my fuse box so I wouldn't have to cut any wires. I used the sun roof for power (always on), the cigarette lighter for on/off (worked with turning the car all the way on), and the first fuse for in the box "panel"? for lighting (worked with headlights). Of note, the lighting on my button doesn't dim with the others, I think the best solution would be to get a "plug and play" wire harness for ~$20 (or cut a wire from a different lighting source). Of course the fuse box cover no longer fits so I'll have to get a Meso customs one if I want to make it clean.

I love the heated seats so far. It works well. It's not nearly as fast as my wife's stock one on her Highlander, it takes it about 3-5 minutes for me to feel the heat when it's all the way up and roughly 10 minutes for me to have to turn it down. I have to turn my wife's down within the first minute of me turning it on. I have my heating pads sandwiched between the cloth seats and Clazzio leather/vinyl seat covers (as recommended by Clazzio). But nonetheless, it's awesome! Thanks again for your help and your great guide.
 
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Thank you for this post! Just got done wiring my heated seats in my 23 offroad and I don’t think there’s a cleaner way to wire them than this.
 
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Thanks for posting these details, OP.

I’ve confirmed I have the heated seats fuse in place in my 21 TRD OR, the empty relay block does have the female terminals installed in it and I am able to find the center console end of IE2, so I’m ordering parts and planning this out.

(I have aftermarket seat heaters already installed, but they tapped into the USB/USB-C charge ports in the arm rest cubby and I want to move them to a different power supply and different switch location).

I am, however, struggling to understand a few key things:

I have Prius switches, which are visually just like yours, a drivers and passengers switch with both low and high, but am not sure how you wired both of them into the center console end of IE2 so they work independently of each other and how the high and low wiring feeds through IE2.

One wiring diagram you posted shows driver side switch wired through IE2 and passenger side wires through IL3, but it appears you combine both seats power wiring and ran them both through IE2? So how do you split the power for the drivers and passenger switched or are you not running them independently of each other?
 
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Thanks for posting these details, OP.

I’ve confirmed I have the heated seats fuse in place in my 21 TRD OR, the empty relay block does have the female terminals installed in it and I am able to find the center console end of IE2, so I’m ordering parts and planning this out.

(I have aftermarket seat heaters already installed, but they tapped into the USB/USB-C charge ports in the arm rest cubby and I want to move them to a different power supply and different switch location).

I am, however, struggling to understand a few key things:

I have Prius switches, which are visually just like yours, a drivers and passengers switch with both low and high, but am not sure how you wired both of them into the center console end of IE2 so they work independently of each other and how the high and low wiring feeds through IE2.

One wiring diagram you posted shows driver side switch wired through IE2 and passenger side wires through IL3, but it appears you combine both seats power wiring and ran them both through IE2? So how do you split the power for the drivers and passenger switched or are you not running them independently of each other?
 
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Sounds like you are overthinking it.

If you already have seat heaters installed, just move the power wires from the USB to IE2 and drop in a relay. The IE2 tap just provides power from the factory location. All the different seat heaters have different wiring but basically you follow those directions and where they tell you to connect to the fuse block or battery, you use IE2.
 
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Sounds like you are overthinking it.

If you already have seat heaters installed, just move the power wires from the USB to IE2 and drop in a relay. The IE2 tap just provides power from the factory location. All the different seat heaters have different wiring but basically you follow those directions and where they tell you to connect to the fuse block or battery, you use IE2.

Ok, I think I understand where we’re straying.

I was thinking you were using the factory wiring, that runs to the center console, to wire in the switches (which would then work through the relay to trigger the power wire to the seats)…but you’re using the aftermarket heated seats wiring for the switches, just replacing the switch itself with the Toyota switch.

The IE2 tap and relay is only to provide switched (ie ignition on) power to the rest of the otherwise aftermarket wiring…

Yep, I was going down a deeper rabbit hole of full stock wiring integration outside of the heating element itself, whoops!

Thanks again and cheers!
 
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Ok, I think I understand where we’re straying.

I was thinking you were using the factory wiring, that runs to the center console, to wire in the switches (which would then work through the relay to trigger the power wire to the seats)…but you’re using the aftermarket heated seats wiring for the switches, just replacing the switch itself with the Toyota switch.

The IE2 tap and relay is only to provide switched (ie ignition on) power to the rest of the otherwise aftermarket wiring…

Yep, I was going down a deeper rabbit hole of full stock wiring integration outside of the heating element itself, whoops!

Thanks again and cheers!
Almost. Mine does not have wiring to the center console.

Different aftermarket systems work differently but on mine the electrical goes IE2 through the switch to the aftermarket relay to the seat heaters. My relay doesn't work like one would expect (separate a high current drawn from passing through a switch). My relay determines if the top heating element and the bottom heating element are in series (low switch setting, high resistence) or parallel (high switch setting, low resistence).

Other systems may want a high current line to go to a relay that is controllerld by the switch. You could use IE2 to both feed a relay in this type of setup as well as to power the switch.
 
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Yep, that’s cleared up for me now. Not sure why I missed the obvious.

I’ll have to figure out how my setup works and adapt it to the Prius switches, but that I can do with my Fluke and a bit of time and some spare wire to extend it all to the center console.

Thanks!
 
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