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Discussion Starter #1 (Edited)
DIY: Retain Navigation w/ aftermarket head unit
Do at your own risk…

Things you will need:
-OEM HEAD UNIT
-Electrical tape
-Blade/Wire stripper
-Philips screw driver
-Zip ties
-Patience

Before you begin, it’s a great idea to locate the wires you are going to be messing with; both on the aftermarket head unit harness and on the stock harness. *Refer to picture in step 6*

These are the wires on the AFTERMARKET head unit harness:
(Use your owner’s manual to figure out the wiring. Wire colors could be different than the ones I’ve stated below)
-12V Constant Power (Yellow)
-Ground (Black) Ground right onto chassis
-Illumination (Orange)
-12V ACC (Red)

These are the wires on STOCK harness:
-12V Constant Power (Yellow/Blue)
-Illumination (Green)
-12V ACC (Gray)

Wiring Diagram/Pinout
2003 Lexus IS300 Wiring Information


KEEP IN MIND THAT I HAVE AN AFTERMARKET SOUND SYSTEM. IF YOU ARE ON OEM SPEAKERS I BELIEVE YOU WILL ONLY BE ABLE TO RETAIN THE FRONT SPEAKERS. WHEN I FIRST DID THIS I WAS ON STOCK SPEAKERS AND WAS ONLY ABLE TO KEEP THE FRONT SPEAKERS.

Steps:
1. Disconnect negative battery terminal

2. Remove your center console to gain access to the back of the radio (I’m not going to go over this. If you don’t know how to do this by now you probably shouldn’t attempt this DIY yourself.) Also, you might want to remove your glove box.

3. Open up your OEM head unit and remove the computer board (This is pretty straightforward. Basically you just need some common sense and you need to keep removing screws until you disassemble everything.)

Tip: The plugs in the rear of the radio are one side of the computer board.

4. Now we move on to the stock harness. Cut and peel back the black insulation on the harness and locate the wires you’re going to work on.

Tip: You’re going to re-route the harness down toward the blower so you should peel the black insulation all the way back to around the base where the harness connects to the chassis.


5. Locate the wires on the stock harness you will be tapping into and splice them. (By splice I mean cut a gap around all of the wire so that the copper is visible, so you can make direct contact with the wires off your aftermarket head unit wires. DO NOT chop the wires completely off lol)


Tip: I used a blade instead of the wire stripper because I was afraid of snapping those really thin wires. Using a blade was probably a bit more difficult but I didn’t want to take any chances. Use whichever you feel more comfortable with.

6. Once you’ve spliced all 3 wires on the stock harness, grab your aftermarket harness. Locate the wires indicated above and match them with the wires you spliced.
-Power->Power
-Illumination->Illumination
-ACC->ACC


7. Use your electric tape and wrap the bare copper wire and past it. Make sure you wrap it tight so it doesn’t come off. After you’ve taped all 3 wires you might want to tape that part of the harness as a whole so its more secure and the wires don’t start pulling.
At this moment your aftermarket harness should be tapped into the stock harness. (Just want to make sure we’re all on the same page)


8. At this point re-route the pigtail of the stock harness down the right side and bring it down into the passenger foot area.


Make sure you’re not tugging on the part where you tapped into and it doesn’t become loose. It shouldn’t be a problem but its better to be cautious.

If you spliced into the stock harness down enough like I said, you should be able to plug in your head unit without a problem even after re-routing the stock harness.


9. Grab the computer board from the stock head unit and find a place to put it under the blower. Use zip ties to secure it.
Tip: Make sure the plug side of the computer board is facing inside toward the harness.


10. Plug in the stock harness to the computer board.

11. Double check everything and make sure nothing is out of place or undone.


12. Connect the negative battery terminal and turn on your IS. Make sure everything works correctly before putting your whole dash back together.

13. Turn your key to ACC and make sure everything works correctly.


14. Turn on your headlights and make sure the nav and head unit adjust to their day/night illumination.
Note: If its bright out, cover the sensors on the driver side dash and make sure the illumination changes.


15. Enjoy your nav and head unit set up!


16. Send me something nice in the mail :)
 

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I tried the method of installing the Computer board under the dash in order to keep my OEM Nav with my aftermarket radio but the Nav screen just says "Lexus" and no sound comes from the speakers. If I unplug the navigation screen completely from its harnesses I will hear sound. Here is how I did my set up:

I kept the original harness coming from the car intact and plugged my aftermarket stereo and amp bypass interface harness into it. I then ran a harness from computer board and spliced into the harness coming from the car. The only wires I spliced into were the constant power, ground, TX+ & TX-, & accessory.

Am I missing something? Any help would be greatly appreciated.
 

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Discussion Starter #3 (Edited)
I was asked about this recently so I wanted to add a diagram. You can also ground the aftermarket head unit to the chassis, and not directly onto the stock radio harness. That's why the pictures in this DIY only show 3 wires that tap into the stock harness.

This can also be done without an aftermarket amplifier, but you will only be able to keep the front speakers by running them off the aftermarket head unit's built in amplifier.
 

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How far down did you strip the oem radio? I left the bottom half of the radio cover (the metal part) on including the antenna plug. I just did this today and only the Lexus logo pops up and then the whole screen shuts down. Did you or anyone else run into this problem with a fix? I have aftermarket speakers, 4 channel amp, and radio as my setup. Thanks
 

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Discussion Starter #5
How far down did you strip the oem radio? I left the bottom half of the radio cover (the metal part) on including the antenna plug. I just did this today and only the Lexus logo pops up and then the whole screen shuts down. Did you or anyone else run into this problem with a fix? I have aftermarket speakers, 4 channel amp, and radio as my setup. Thanks
Is your wiring the same as mine? Did you connect the radio harness into the stock radio board?

All that was left of my stock radio was this, with the 2 plugs on the side

Where in so cal are you located?
 

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Hi, I'm very interested into doing this, sorry for the super late reply: Will the joystick/buttons still work under the shifter to control the GPS? Thank you in advance
 

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Discussion Starter #7
Hi, I'm very interested into doing this, sorry for the super late reply: Will the joystick/buttons still work under the shifter to control the GPS? Thank you in advance
Yes, nav controls still work. Everything remains the same. I have the OEM nav remote and it works as well.
 

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Discussion Starter #9
did you put custom lighting on your cig and driving gears? Don't think I've ever seen that before.
All interior lighting has been replaced with red and white LEDs. I did it after this DIY so not visible in these pics.
The instructions to change lighting are on this forum.
 

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Hello is family, I just recently ran into the issue that member homedepotmade ran into 3 years. After performing all the above steps my nav screen powers on shows the Lexus logo then shuts off. Did anyone figure out the solution to this?
 

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Thanks for this wiring diagram, it makes much more sense than your initial directions. I am unclear on 2 things:

(1) how does the sound from the navigation (directions like "in 300 feet, turn left") get to the speakers? You show the speakers wired up to the amplifier, and the only spliced-in wires are power, acc, illumination, and ground. Do the voice commands from the navigation work?

(2) Why do you need a discrete amplifier to run the back speakers? Aftermarket head units have 4 channels, and the stock wiring harness has 4 wire pairs to FR, FL, RR, and RL. Without navigation, you'd simply hook up the head unit to those 8 wires, but it doesn't look like you are showing the stock speaker wiring harness at all. Is the "stock harness" connecting to the OEM computer board actually more than 4 wires?
 

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Discussion Starter #12
Thanks for this wiring diagram, it makes much more sense than your initial directions. I am unclear on 2 things:

(1) how does the sound from the navigation (directions like "in 300 feet, turn left") get to the speakers? You show the speakers wired up to the amplifier, and the only spliced-in wires are power, acc, illumination, and ground. Do the voice commands from the navigation work?

(2) Why do you need a discrete amplifier to run the back speakers? Aftermarket head units have 4 channels, and the stock wiring harness has 4 wire pairs to FR, FL, RR, and RL. Without navigation, you'd simply hook up the head unit to those 8 wires, but it doesn't look like you are showing the stock speaker wiring harness at all. Is the "stock harness" connecting to the OEM computer board actually more than 4 wires?
1.I did not want the nav voice commands so I didn't bother with wiring it. From what I remember reading, you can find the schematics and use the mute function, which mutes the drivers speakers to hear voice commands.
2. I'm running aftermarket amps so I don't need to run my speakers off the aftermarket head unit. Need more juice for my aftermarket speakers.
 

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I bought an IS300 recently and the car has the Nav unit on top of the dash but the car came with a aftermarket double din head unit. I was interested in making that Nav unit in the middle to work and I came across this thread. What I'm wondering is, do I need a factory radio unit from a car that had the Nav unit or any IS200/IS300 stock head unit will work?
 

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Discussion Starter #14
I bought an IS300 recently and the car has the Nav unit on top of the dash but the car came with a aftermarket double din head unit. I was interested in making that Nav unit in the middle to work and I came across this thread. What I'm wondering is, do I need a factory radio unit from a car that had the Nav unit or any IS200/IS300 stock head unit will work?
Any stock head unit
 

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Having similar issue. lexus logo shows up and then turns off. any solution?

Did u just use this board from radio?


or did you include the CD driver too?


*** UPDATE ***

It's fully working now. Thanks a lot. It was probably a loose connection or something. everything is working fine. Thanks for a great DIY.
 
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