Retrofitting heated seats and illm wire?

Discussion in 'Gen 4 Prius Accessories and Modifications' started by mjoo, Dec 23, 2019.

  1. mjoo

    mjoo Senior Member

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    Hi Everyone,


    I spent the past couple of days retrofitting heated seats to my wife's 2016 Toyota Prius and have everything done except for connecting the wires on the harness. There are 4 wires: power (red), ground (black), acc (red with yellow) and illm (yellow). I know how to connect the first three but the illm I'm not so sure where to connect it. All the manual says is this illm wire "connects to car interior light's positive electrode." Where should I connect the yellow illm wire to? What's the purpose of the illm wire? Thanks in advance.
     
  2. ChapmanF

    ChapmanF Senior Member

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    Looks like an abbreviation for 'illumination', i.e., the circuit that makes your heated seat switch light up so you can see where it is to turn it on. For the most 'integrated' look, you would find wires that are on the car's dash illumination circuit, the one that is dimmed by the knob on the panel. The wiring diagram (more info) will show you where to find those. If you have a lower trim, you can probably find it on existing unused connectors behind the dash, such as for the headlight washer button in cars without headlight washers.

    It sounds like your seat kit wants a positive 'illm' wire, and will reference it to a common ground. I've had at least one car where the dash light dimmer circuit actually went between the lights and ground, rather than between the + supply and the lights. I've forgotten whether my Gen 3 is that way or not ... I must have looked it up in the wiring diagram when I put in the switch for my inverter, but now I'm drawing a blank and would have to look it up again.
     
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  3. mjoo

    mjoo Senior Member

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    Do you think the "illm" wire is a 0-12V analog reference for a dimmer circuit? What you say makes sense. Then would you think the backlight dims as the "illm" voltage goes up?

    I was on TIS last night downloading all sorts of Gen 4 manuals. I'm waiting on a reply to last night's email to Sojoy, the heater manufacturer.

    It's interesting that for the Gen 3 Prius, Toyota has Prius Seat Heaters installation instructions (PZ457-G0311-00) that tells you to connect a blue wire to the ILLUMINATION signal - pin 18 on the ECU below the dash. However, this doesn't help me. Looking through the electrical schematics on TIS (I subscribed last night) I couldn't find an ILLUMINATION pin. I'm also still looking for Gen 4 seat heater instructions. Maybe I'll cross-reference pin 18 in the Gen 3 manuals and find what that's used for. Maybe it's actually part of the map or rear dome light circuit.

    BTW, I can send you the Gen 3 instructions if you're interested...

    Another smaller question for those that have modified - have you found it better to run a power wire directly to the battery than tap into the fuse box?


    Gen 3 seems more aftermarket friendly. There were also blank switch positions on Gen 3 that were replaced with (programmable) switch assemblies on Gen 4.
     
    #3 mjoo, Dec 24, 2019
    Last edited: Dec 24, 2019
  4. ChapmanF

    ChapmanF Senior Member

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    I wouldn't expect it to be anything complicated; it's probably just a wire leading to one side of whatever light or LED is inside your heated seat switch.

    Have you looked closely at the switch itself? Sometimes they have both legs of the illumination lamp brought out to separate terminals, not shared with any of the switch contacts. That gives you the most flexibility for wiring. In some cases, they might assume one of the switch terminals will be grounded, and common one leg of the light to that, leaving only the other leg for you to hook up to a supply some time, which you would have to connect to a +12 supply (or a dimming supply, +12 at full brightness).

    Or, they might assume one of the switch terminals will be getting +12, and common one leg of the light to that, so the one left loose for you would have to be connected to ground (or to the kind of dimmer that goes on the ground side of the light).

    Now that you have the diagrams from TIS, you should be able to look at the circuits for all the other various dimmed lights in the dash, and that will show you whether the existing dimmer in there is the kind to go between +12 and the light, or between the light and ground.

    You've got the primary reference material now that you've got your own year's wiring diagram. Just look up a few of the dimmable lights in the dash and trace back to what's supplying them. If you're lucky there will be some unused connectors behind some of the unused switch blanks on your dash, and the wiring diagram can show you (by pin number and by color code) which wire at one of those connectors will be the illumination circuit. Then you have a super easy place to tap. (I sometimes just extract that wire, terminal and all, from the unused plastic connector, and slip it, terminal and all, into a barrel of a Euro-style terminal block, with a wire off to my added circuit going off from the same barrel. With a little care to insert the original far enough that the screw clamps down on the crimped part, not the shaped part, the car can later go back to fully stock just by clicking that terminal back into its original connector.

    [​IMG]

    In a Gen 4, that would mean a firewall penetration, right? Sounds like too much hassle to me. There will already be at least one heavy wire bringing that in through the firewall to your inside fuse box (wiring diagram will have details); you might find that there is some unused fuse position that will already work if you put an appropriately-sized fuse there, or you might tap off the input side of the box. Doing so, you're already protected by the fuse link on the battery side of that cable, saving you one detail that you'd have to attend to if connecting to the battery yourself.

    Knowing the total draw of your seat heater will help make the right decisions....
     
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  5. mjoo

    mjoo Senior Member

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    Ok after a few hours getting used to TIS and collecting some interesting TSBs, I found the factory heated seat component locations. It turns out that Toyota connects their ILL pin (turns on the backlight of the seat heater switches) to the TAIL relay. They connect their IG to IG1 No. 4 Relay. I also found that power, ACC, and ILLM can be connected to fuses in the panel below the dash.

    The only thing left to do is figure out what I will use to tap into the relays. I bought 2 tap-a-circuits for the mini fuses (all they had) but for those signals that don't require much power (IG1, possibly ILL) maybe I can come up with a more elegant solution. A wire soldered to a fuse comes to mind.
     
    #5 mjoo, Dec 24, 2019
    Last edited: Dec 25, 2019
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  6. ChapmanF

    ChapmanF Senior Member

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    How many connectors and/or junctions do the factory seat switches go through on the way to IG1 No. 4? Are any of those present and easy to reach in your car? Maybe with an empty terminal position at that spot? Get the proper repair terminal from the dealer (see the part number by clicking the {Wire Harness Repair} link in the EWD page for that connector), crimp to your aftermarket seat heater IG wire, click into the connector in the proper position. Elegant and reliable.

    Same approach can work for the other circuits.
     
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  7. vvillovv

    vvillovv Senior Member

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    On the Gen 3 (the Plugin anyways) could explain some of the confusion in the manuals, the seat heater switches don't have illm, but they do have on low and on high. It is the same with Gen 4, (the Prime specifically) no light on the switch, but low and hi settings for the amount of heat.
     
  8. vvillovv

    vvillovv Senior Member

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    ooops, I finally see the seat heater switch lights. 3 lights on each switch, the illm, a low on and a high on.
    no more feeling around in the dark to find those switches for me... sorry bout that.
     
  9. mjoo

    mjoo Senior Member

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    All the seat heater fuses are preinstalled from the factory. Connectors F24 and F25 are just hanging out behind the "lower center instrument cluster finish panel sub assembly" (what a mouthful) in blank connectors. F24 and F25 contain all the wires I need to connect to.

    Now I need to decide if I want to pull the terminals out of them and clamp them into terminal blocks or cut the harness and splice wires. Lots of options here!
    IMG_20191226_135155.jpg IMG_20191226_144414.jpg IMG_20191226_144218.jpg IMG_20191226_144426.jpg

    Pixel XL ?
     
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  10. ChapmanF

    ChapmanF Senior Member

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    Euro-blocks are cheap and work well, and if you avoid crushing the hollow parts of terminals, completely reversible to stock. :)
     
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  11. mjoo

    mjoo Senior Member

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    Hit a wall. I believe I'm missing "IG1 NO.4 Relay" because fuse "20A S/HTR- MAIN" is receiving power but the fuses "10A S/HTR F/L" and "10A S/HTR F/R" are not receiving power. The repair manual on TIS says "IG1 NO.4 Relay" is in "Instrument Panel Relay Location R/B Assembly No. 4". According to TIS this panel should be located on driver's side above the fuse box in the dash. I have the left hand finish panel off but do not see the relays. Has anyone seen these?
     
  12. mjoo

    mjoo Senior Member

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    Ok I have a solution. Although using the OEM relay in the circuit would ultimately be the cleanest and coolest there's a compromise that would only need one tap-a-circuit. I plan on jumping the 20 A fuse to the two 10A fuses with a couple of short wires - bypassing the IGN 1 No. 4 relay. Then use the relays in the kit and connect their ACC wires to the ECU IGN 1 No 4 fuse under the dash.

    Pixel XL ?
     
  13. mjoo

    mjoo Senior Member

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    Got it working! Thanks for the help @ChapmanF

    Pixel XL ?
     
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  14. vvillovv

    vvillovv Senior Member

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    @mjoo I like the link in your sig Cleaner, quieter engine
    I went to the walmart and got a 2 oz bottle of their cheap stuff to use as a measuring container. I'm going to try the formula out in our 02 civic first.
    When reading about the research, it brought me back to the days my dad used to feed marvel mystery oil straight into the carbs while running the engine. It would smoke like the engine needed new rings on all the pistons for a few minutes as long as he poured it in slow enough not to stall it out. When my dad did that it would always remind me of the Mosquito Bug Spray trucks that used to go up and down the streets in August.

    Thanks for the time and effort you and the team at ls1 put into the research and testing.
     
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  15. mjoo

    mjoo Senior Member

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    Good! Yeah, I think TCW3 is even more helpful today with the additional ethanol in the fuel.


    Pixel XL ?
     
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  16. Gicone

    Gicone New Member

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    Hello! Im trying to make the retrofit for gen3 and I can’t find any electrical wire scheme. I bought a second hand interior. From what I see I’m missing 2 Wire from each front seat. Can someone help me where should I connect the 2 wires?
     
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