Author Topic: FAQ: Lexus IS250 Steering Wheel Retrofit for 1994-97 Supra  (Read 4281 times)

May 21, 2013, 09:55 PM #0

Eden Offline

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This guide will take you through retrofitting a 2008+ Lexus IS250/350 steering wheel into a MKIV Supra with a 94-97 style steering wheel.  The paddle shifting and rolling antilag portions are specific to ProEFI users... but I think I'm the only one in Winnipeg with one :P

I'll break the FAQ into a few sections and throw in pictures/tables/etc. to help with understanding all the steps.  This took me an entire day to map out, even with pointers so please enjoy to the fullest.

What is needed:

2008+ Lexus IS250/350 steering wheel with paddles and buttons
2006+ Lexus IS250/350 airbag
Lexus IS300 airbag (we will only use the ignitor cartridge on the back)
PAC-SWI RC (Steering Wheel Audio Interface)
PLCC-2 white LEDs (I'll double check how many again) for button illumination (OEM:green)

Quality soldering iron: preferably with temperature control
Optional: Smoke absorbing puller fan (don't want lung cancer...)
63/37 rosin core solder
Flux syringe
Heat gun
Mechanical helper hands (so awesome!)
Straight edge cutters
Wire strippers
Needle tip tweezers
3 sizes of Phillips head screwdrivers
Small flathead screwdriver

1/4W Resistors: 180, 220, 270, 560,
Resistors from old 94 style steering wheel for straight swap
  *NOTE: 98 style wheels use the same resistors and so a swap wouldn't be necessary*
Bunch of 22ga wire, different colours help
Lots of 3/32" shrink tube

======================================

OEM Steering Wheel Harness

-Snip it right off.  Here's a table I made of all the pins, colors, functions, and the plan!
*Note: Yellow wire (Disp) will be used as the Rolling Antilag button! :D  It will splice away before the PAC-SWI to the ProEFI  on an Analog pull-up resistor Input.



Here is a scan of the LH and RH audio controls.  It doesn't show the Display button.  I have mapped out all the resistors and overlaid them in red for your curiosity!


======================================

Paddle Shifters for use with ProEFI

This is a basic diagram I made, showing, basically, how the shifters are wired up.  Resistor R1 is optional, but I put it in there anyway.  This method allows us to use a single input and each switch has a different resistance value that the ProEFI can read to differentiate the upshift VS downshift.



======================================

Cruise Control (I believe you just need to solder in red-red and black-black on 1998 style)

(1994 style steering wheels only)
There are 3 wires from the factory and you'll only be using two.
-Connect White/Black from the old stalk to White on the IS250 stalk.
-Connect your Red/Yellow and Light Blue wires together from the old stalk and then solder to Red on the IS250 stalk.
-Remove the three resistors found on the board. 
-Apply flux to the pads
-Replace with the resistors from your 1994 style steering wheel cruise control.





======================================

Airbag

The IS250/350 airbag is two-stage so it has 4 connectors.  We will convert it to a single stage by swapping over the ignitor cartridge from an older Lexus IS300.  It is an identical fit but it's single stage, so it only has 2 wires like our beloved Supra airbags.

I'll have more on this Thursday when I get my IS250 airbag in.
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    May 21, 2013, 09:56 PM #1

    Eden Offline

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    Reserved for pics and videos by the weekend.
    USDM MKIV Supra - 800BHP / 636RWHP at 20PSI on E70 through a Titan-built automatic.  3.2L stroker, Borg Warner S363

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      May 21, 2013, 10:15 PM #2

      Commanderwiggin Offline

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      Looks like a ginormous PITA!
      900rwhp Turbo E46 M3
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        May 21, 2013, 10:48 PM #3

        Eden Offline

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        Oh, it was...  Took me all afternoon to figure it all out.  I had very little info to begin with and the wiring diagram from Lexus I drove across town for was only a little helpful, so I ended up studying all the circuits, measuring all the resistors, etc.  The conversion itself wouldn't take more than an hour or two now that this guide exists :P
        USDM MKIV Supra - 800BHP / 636RWHP at 20PSI on E70 through a Titan-built automatic.  3.2L stroker, Borg Warner S363

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          May 21, 2013, 11:08 PM #4

          Commanderwiggin Offline

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          Originally posted by Eden
          Oh, it was...  Took me all afternoon to figure it all out.  I had very little info to begin with and the wiring diagram from Lexus I drove across town for was only a little helpful, so I ended up studying all the circuits, measuring all the resistors, etc.  The conversion itself wouldn't take more than an hour or two now that this guide exists :P

          LOL good work
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            May 22, 2013, 08:01 AM #5

            Winter Beater Offline

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            Looks like fun!!

              February 24, 2014, 10:55 PM #6

              Adrianross Offline

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              I've taken the resistors out of the 95 MKIV cruise control lever and placed them into a 2000 model cruise control lever. I attached the old white/black to the white from the new lever and the other two wires to the red from the new lever.

              When connected the cruise on/off button is depressed resulting in a blinking cruise light. When the lever is moved up or down, the cruise light will respond by turning on or off accordingly.

              Needless to say, I think I've lost at plug n play directions and will need to dive in to the circuit. If you are still checking this post, I think it would be great if you could share some insight or possibly any existing wiring diagrams you may have of the switches. I feel like I'm on the right track, just need a little bit of help.

              I hope you don't mind rehashing an old post! Thanks!
              Last Edit: February 24, 2014, 10:57 PM by Adrianross

                February 25, 2014, 11:01 AM #7

                Eden Offline

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                Hey Adrian, in testing, I never got the cruise control to work correctly, but I did get the audio controls, horn, airbag, LED's (swapped mine for white PLCC-2) and shifters working correctly.  I had thought up a way to make it work but then I got side tracked with other projects and never went back in.  I'll need to dig up my old wiring diagrams again and update this.  Thanks for reminding me.
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                  February 25, 2014, 11:27 AM #8

                  Adrianross Offline

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                  That is actually great to hear! I thought I had done something wrong. I am glad to help get this completed. Here is a diagram of the 98 Supra if its needed. The 93-96 may however be what is really called for in this scenario as we are attempting to convert the cruise control switch to that year model. A diagram for the 2000 Toyota Celica or Lexus cars that use the same style cruise control switch could help here as well. I'll try to look while waiting to hear back from you.
                  Last Edit: February 25, 2014, 10:17 PM by Adrianross

                    February 26, 2014, 02:54 PM #9

                    Eden Offline

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                    That jogs my memory a bit.  So the issue is that we're combining the CMS wire (only present on pre-98 models) which tells the ECU to turn ON cruise control, with the CCS wire.  The CCS wire goes to a pull-up resistor input.  So depending which switch button you press, it reads a different current because of the different resistor values in the cruise stalk, which we addressed with the resistor swap I documented above.  Problem is that by combining the two, the signal that should only be going to the CCS is also being fed to the CMS and messing things up.  The only way around it that I see is to remove the CMS wire from the circuit and let the cruise stalk go straight the CCS only.  Then wire the CMS wire to a momentary switch elsewhere to toggle cruise control On/Off.  That should fix it.


                    Edit:  Or else keep the 94 style cruise stalk and physically modify it to fit...  Whichever is easier.

                    Update also on the rest: 
                    By combining the LH and RH side audio controls, there is a signal conflict between some of the buttons on the right when they are all wired to the PAC controller.  So basically, some resistor values need to be changed because some signals are too similar.  Moreover, there is an issue with programming the signal values with the car running, on accessory mode, with/without headlights or fog lights on, etc because these conditions alter the output of the electrical system.  Using the capacitor that comes with the PAC and programming it with the car running and headlights off should resolve this issue, but I have yet to wire it in.  In the meantime, simply not programming the Mode button or the RH side buttons will alleviate the problem but limit your controls.

                    Also, similar to the cruise control problem, you cannot splice out two outputs from the same buttons.  The current tends to follow the path of least resistance, or else just gets messed up and nothing works.  So rather than splicing the PAC and the Rolling Antilag inputs along the same wire, you need to put a switch after the buttons, but before the PAC and the ECU input for Rolling Antilag.  That switch will basically remap the functions for the steering wheel controls.  When switched one way, they will control audio functions.  When switched the other way, it will control two step and rolling antilag along with any other function you want to use the input for.  The ECU uses a pull-up resistor in the same way as the PAC, so once you know the ADC values, you can use whatever steering wheel button for whatever ECU function.
                    Last Edit: February 26, 2014, 03:40 PM by Eden
                    USDM MKIV Supra - 800BHP / 636RWHP at 20PSI on E70 through a Titan-built automatic.  3.2L stroker, Borg Warner S363

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                      March 20, 2014, 07:26 AM #10

                      Joe Offline

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                      How much were you able to find a is250 wheel for? 
                      Great write up
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                        March 20, 2014, 01:06 PM #11

                        Eden Offline

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                        I found a good one on Ebay, but I forget what the price was.  All said and done, I think I paid around 1000$ or so.  That includes is350wheel with buttons/paddles, is350 airbag (the most expensive part), is300 airbag (just to pilfer/remove its igniter cartridge).  The new white LEDs for the audio buttons were cheap too.  Later on, I may upgrade the wheel with enhanced contoured leather and CF, but that's a low priority.  Would be another 600$ or so.
                        USDM MKIV Supra - 800BHP / 636RWHP at 20PSI on E70 through a Titan-built automatic.  3.2L stroker, Borg Warner S363

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                          March 26, 2014, 12:18 AM #12

                          Adrianross Offline

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                          Eden, I finished re-working the wiring today. The CRUISE-ON/OFF trigger button works correctly. RES/ACC (up) has a 95ohm read out, identical to the OEM 94 cruise lever. SET/COAST (down) however is reading between 265-295ohms where as the OEM 94 cruise lever reads a solid 255ohms.

                          I plan to test the unit in the morning/afternoon and report back on the functionality. If you see any issues with the ohms readings, go ahead and shoot me your thoughts.

                            March 26, 2014, 01:15 PM #13

                            Eden Offline

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                            That's weird that you're getting messed ohm readings on one.  Did you use the original resistor from the old cruise stalk?  Or maybe try replacing with a new 255ohm resistor?  Could be a bad solder joint.  Maybe see if you can clean it up with some flux and a reflow?
                            USDM MKIV Supra - 800BHP / 636RWHP at 20PSI on E70 through a Titan-built automatic.  3.2L stroker, Borg Warner S363

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                              November 28, 2014, 12:45 AM #14

                              Adrianross Offline

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                              UPDATE: issues preventing me from completing the circuit correctly for cruise control were due to series differences between the 2000 cruise lever and 2008. Honest mistake on my end, I simply didn't pay attention to the physical differences between what I had, and what was posted here. I've since had both in my hands and modified them to work as intended with the 93-98 Supra in an OEM fashion with no tricky wiring.

                              Option 1: Fitting a 2008 IS steering wheel with paired 2008 IS cruise lever to a 93-98 Toyota Supra
                              Step 1: Tear down the cruise lever as shown in OP's first thread post
                              Step 2: Remove resistors. Since they are single pulse spot welded, you have to pull and bend them until they break off. Soldering iron will not remove them, do not try.
                              Step 3: Harvest the correct resistors from your existing Supra cruise lever. If you have a 93-96 Supra lever (or most any mid 90's Toyota lever) to harvest resistors from, you will need to use a dremel tool to grind out the appropriate space for the resistors to sit as they are 2.5 times the size of the IS resistors.
                              Step 4: Once a space is adequately dremeled out, the method which you employ to adhere the resistors is up to you. To do this professionally,  you can use a single pulse mini spot welder. I didn't have access to one, so I simply applied flux, applied solder, then used a series of tools to press and seal the resistor tips into the solder. If I made this part sound easy, I apologize; this is the most difficult part of the entire process and for an amateur may result in the demise of said cruise lever circuit board. Be patient and cautious and you will be rewarded.
                              Step 5: Remove connection from point "A" and re-solder to point "B" in photo below.
                              Step 6: Ohm out the circuit in a series fashion. Using the same resistor installation diagram photo:
                                 6a: place a probe at the bottom of resistor #1 and the top of #2, you should get  roughly .96
                                 6b: place a probe at the bottom of resistor #1 and the bottom of #3, you should get roughly .256
                                 6c: place a probe at the bottom of resistor #1 and the top of #3, you should get roughly .482
                              Step 7: Reassemble and solder the wire tips as follows from cruise lever to Supra connector:
                                 Black -- White w/Black
                                 Red-- Red
                                 White -- White
                              You are done, install and enjoy cruise control !!!



                                November 28, 2014, 01:01 AM #15

                                Adrianross Offline

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                                Option 2: Fitting a 2000 Celica steering wheel with paired 2000 Celica cruise lever to a 93-96 Toyota Supra
                                Step 1: Tear down the cruise lever in similar fashion to OP's first thread post
                                Step 2: Remove resistors. Since they are single pulse spot welded, you have to pull and bend them until they break off. Soldering iron will not remove them, do not try. Note where you moved them from as I have not included a photo of this circuit.
                                Step 3: Harvest the correct resistors from your existing Supra cruise lever. If you have a 93-96 Supra lever (or most any mid 90's Toyota lever) to harvest resistors from, you will need to use a dremel tool to grind out the appropriate space for the resistors to sit as they are 2.5 times the size of the celica resistors.
                                Step 4: Once a space is adequately dremeled out, the method which you employ to adhere the resistors is up to you. To do this professionally,  you can use a single pulse mini spot welder. I didn't have access to one, so I simply applied flux, applied solder, then used a series of tools to press and seal the resistor tips into the solder. If I made this part sound easy, I apologize; this is the most difficult part of the entire process and for an amateur may result in the demise of said cruise lever circuit board. Be patient and cautious and you will be rewarded.
                                Step 5: Ohm out the circuit in a series fashion. Using the same resistor installation diagram photo below as reference, you will be able to understand the process.
                                   6a: place a probe at the bottom of resistor #1 and the top of #2, you should get  roughly .96
                                   6b: place a probe at the bottom of resistor #1 and the bottom of #3, you should get roughly .256
                                   6c: place a probe at the bottom of resistor #1 and the top of #3, you should get roughly .482

                                Step 6: At section "3" in the photo below, separate the Black and Red wires from their bonded connection beneath the electrical tape.
                                Step 7: Reassemble and solder the wire tips as follows from cruise lever to Supra connector:
                                   White -- White w/Black
                                   Red-- Red
                                   Black -- White
                                You are done, install and enjoy cruise control !!!

                                I have done this successfully for roughly 10 people and they all work flawlessly. Good luck, and Eden I thank you most respectfully for allowing me to add to your write up.




                                  January 10, 2015, 05:54 PM #16

                                  Eden Offline

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                                  Awesome job man, thanks for helping answer some of the important details :)  I'll have to swap over point A to point B (something I don't believe I had thought of.)  Hopefully that'll be the missing link for my cruise.  Thanks so much for helping!
                                  USDM MKIV Supra - 800BHP / 636RWHP at 20PSI on E70 through a Titan-built automatic.  3.2L stroker, Borg Warner S363

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                                    January 15, 2015, 05:04 PM #17

                                    Adrianross Offline

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                                    I have to update the photo, turns out there are two models of that particular cruise lever. One has a 4th function to set the radar cruise computer and it uses that set up, but if you have the non-radar version, you actually LEAVE "A" and move the far side to "B". I'll post the pics up possibly by tomorrow :)
                                    Last Edit: January 15, 2015, 10:28 PM by Adrianross

                                      January 21, 2015, 05:22 PM #18

                                      Adrianross Offline

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                                      Can you take a look at this diagram Eden? I have routed the wires as so:

                                      White - Ground
                                      Brown - Goes straight through to the SWC controllers resistive input preceeded by a 110ohm resistor
                                      Red - enters brown after the resistor, and is also resisted at 389ohms
                                      Gray - enters brown after the Red wire and is resited at 560ohms
                                      Yellow - enters brown after Gray and is residted at 194ohms

                                      For some reason I get the same resistive value for the Volume down button as I do for the Left function.

                                        January 24, 2015, 05:57 PM #19

                                        Eden Offline

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                                        Between which points are you measuring the resistance to and from when comparing left and volume down?
                                        USDM MKIV Supra - 800BHP / 636RWHP at 20PSI on E70 through a Titan-built automatic.  3.2L stroker, Borg Warner S363

                                        http://TheraVape.net
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                                          FAQ: Lexus IS250 Steering Wheel Retrofit for 1994-97 Supra
                                          « Reply #19 on: January 24, 2015, 05:57 PM »