DIY: Retain Navigation w/ aftermarket head unit
Do at your own risk…
Things you will need:
-OEM HEAD UNIT
-Philips screw driver
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
-12V ACC (Red)
These are the wires on STOCK harness:
-12V Constant Power (Yellow/Blue)
-12V ACC (Gray)
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.
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.
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