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

[Asmara]

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.

 

[Athena32]

Interesting. So they’re using the resistance of the elements to effectively lower the amount of current through the circuit. In turn, the elements run at a lower wattage. If they run them in parallel, the resistance of the elements isn’t factored in because the elements are being driven independent of one another. That’s smart—credit where credit is due.

The Clazzio kit looks similar to yours; I’d bet they’re the same manufacturer. I modified my harness today and I think I understand what you mean about connecting the switches together. For me, there’s an illumination wire and a switch power wire. As opposed to having two connections that run to vehicle circuits, you can have one if you tie these two connections together at the switch. This is ultimately what I ended up doing.

After much consideration, I think I’ll pull the switch power from the in-cab fuse block—likely Power Outlet 1 or 2. The illumination wire I can find behind the radio I believe. The main power for the elements will come from an in-cab electrical distribution panel I have installed.

Thanks for the reply. That tidbit about how the elements work is very enlightening.

 

[oscarmeyers]

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.

Did you replace the led's to green? If so where did you buy them and were they hard to change?

 

[Asmara]

Did you replace the led's to green? If so where did you buy them and were they hard to change?

No. I didn't. When I was looking at the lighting, I realized that the defroster and mirror heaters were both orange so I figured it was more factory to leave them. I haven't cracked open the switches in a while but when I was playing with the blue LEDs, I bought them from www.KingbrightUSA.com. You want 4.0x4.0mm right angle LEDs. They run about 50 cents each. They are surface mounted but pretty easy to take on and off with minimal skill.

 

[oscarmeyers]

Thank you sir.

 

[Proudy202]

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.

Thankyou for this! I'm all for a clean OEM looking install and this is by far the best install I've seen for heated seats! (I'm not a massive fan of an add-a-fuse)

I've got everything ordered and am about ready to install I was just wondering if you could clarify a couple of points. I'm mechanically minded but the dark arts that are electrical always send my head into a spin (it took me sometime to realize you were leaving the aftermarket relays in place and just using the factory relay and fuse as a power source!!)

I've ordered a switch T-Harness for below the head unit to get the illumination power to the seat switches.

Did your heater wiring have 4 wires in it? I have the heavy fused power, ground, illumination and a 4th wire labelled 'on wire' I guess this is for an ignition wire?

With regards to splicing the 2 power wires together did you remove the fuses, my thinking is they're redundant now it's all being powered through the factory fuse? But something is telling me the extra fuse is a good safety measure?

Thanks
Ash

 

[Asmara]

I removed the fused because I was using the factory fuse. You don't want redundant fusing because it makes troubleshooting really hard. You especially don't want fuses buried in your dash. Just use the factory fuse.

I didn't have wiring similar to yours. It sounds like your 'on' should be on an ACC circuit (live when the truck is running) that goes to your switch, then from the switch to the relay. That low amp 12v will be used to trigger the relay that will pass the 'heavy fused power' to the seat heaters. This is different than how my system was designed by the factory.

 

[Proudy202]

I removed the fused because I was using the factory fuse. You don't want redundant fusing because it makes troubleshooting really hard. You especially don't want fuses buried in your dash. Just use the factory fuse.

I didn't have wiring similar to yours. It sounds like your 'on' should be on an ACC circuit (live when the truck is running) that goes to your switch, then from the switch to the relay. That low amp 12v will be used to trigger the relay that will pass the 'heavy fused power' to the seat heaters. This is different than how my system was designed by the factory.

Thanks! Yeah I've just been looking at the wiring, you're right the 'on' goes straight into the switch, this makes sense now, I'll just tap into a wire in the T-Harness so It remains as plug and play as possible!

Thanks for the quick response!

 

[roderickhughes]

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.

Great post and thank you, I am right in the middle of my install and have one quick question. I am using the Denso relay you mention, but also my clazzio seat heaters came with relays in the harness, should I remove them from the circuit or keep them there? any help appreciated

 

[Asmara]

It depends on what the relays are doing. If you read through the thread, you will see that my harness uses the relays to control the wiring path to switch between low and high. Relays are more frequently used to switch high current loads that might burn up a switch.

If you have a wiring diagram, I could take a look at it. Even a picture of the wiring laid out might give me enough info.

 

[roderickhughes]

I will work this tonight and thank you for the reply! My issue is that I blew a fuse bing sloppy. I can confirm this works fine with the clazzios leaving all stock wiring/relays.

 

[Asmara]

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. A Athena32 posted above about a Clazzio install using this technique and may answer a PM.

 

[roderickhughes]

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)

 

[TacoTeflaro]

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?

 

[Asmara]

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.

 

[YodaC]

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?

 

[Asmara]

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.

 

[TacoTeflaro]

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.

 

[bbrowning620]

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.

 

[Jmanscotch]

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?

 

[Asmara]

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?