Here are the steps for installing a manual cutoff switch for temporarily disabling the speed signal going to the head unit on your ES350.
I believe drivers should be able to choose whether or not they can safely operate the features that Lexus automatically disables when moving (dialing phone numbers, viewing MP3 filenames, etc.). The Lexus nanny lockouts are too restrictive and responsible drivers are quite capable of safely operating these features. Having said that, ANY distraction while driving is potentially a deadly one, so let the user beware! Be safe. Don’t even think of viewing DVDs while driving.
The nav map without the input of the speed signal doesn’t move smoothly because the car is relying on GPS information only. The car locator may also be inexact (but close) in its positioning. Turning the speed signal back on restores normal operation. You can switch back and forth between normal operation (speed lockouts on) and cutoff active (speed lockouts off) without interrupting any nav functions, such as route guidance. However, I recommend using only normal operation when near route guidance instruction points (i.e. turns) to avoid any chance of error.
You can use any SPST (single pole, single throw) switch - rocker, toggle, or button. If you want your switch to be illuminated to indicate whether or not the cutoff is active you’ll need a DPDT (double pole, double throw) switch. Don’t run the current for the LED on the same circuit as the speed sensor.
I used an illuminated rocker switch from DigiKey (part # 67-1933-ND) because it matched the nearby switches and I wanted an LED indicator. This switch is SPST, but I modified it to function as an inverted DPST switch. This was a lot of work and I do not recommend you do this. Just buy a DPST switch and save yourself the effort.
I used insulated blade connectors to make all my connections. You will need an inexpensive crimping tool to attach them to your wires. They are quick and easy and allow the original wiring setup to be restored quickly.
This is the back of the head unit. The light blue wire just inboard of the outer yellow wire in the top right harness is the speed sensor wire. Cut this wire and connect each end to the wires going to your cutoff switch. Use a male & a female connector on the original wire so you can easily undo your changes.
I pulled back the black vinyl tube and made my cut & connections underneath, so that afterwards I could slide the vinyl tube forward over the connection. This protects the connection and is much neater. Plus you can remove the custom wires, reconnect the blue wire at this point, and cover all evidence of the former modification.
Run the two wires under the dash to your switch location. Use cable ties to hold the new wiring. If youíre satisfied with your work so far, reinstall your head unit by reversing the disassembly steps.
I chose to mount my switch in the switch cluster to the left of the steering wheel because it was easy to do and there was an available place for the switch. If you have parking assist then you donít have room here and will have to locate your switch somewhere else. It can be anywhere convenient for you. This switch panel easily pries off (the photo was obviously taken after installation).
Make a paper template of the cutout needed for your switch and use a razor knife to make the cutout. Remember the hole should be about the size of the switch body, not the faceplate. The bulges in my cutout are to accommodate my switch modifications. FYI, the cost for this switch plate from Lexus is $50. Yikes!
These are the four new connections at the back of the new switch. If you have a non-illuminated switch youíll have only two wires. The red and white wires here (these are my wires) run between the switch and the cut speed sensor wire behind the nav unit. Use a male and a female connector on the nav side of the red and white wires so you can easily restore the speed sensor circuit should your switch ever fail, or to permanently restore stock operation without having to disassemble the head unit again. The black and green wires are power and ground for the LED. If you donít have an illuminated switch you donít need them and can skip the next two steps.
If you do have an illuminated switch, cut into the black wire between the yellow and brown wires in the unused parking assist harness and connect the wiring side to the power terminal on your switch. You can leave the remaining inert harness-side wire bent up like this (black wire in middle).
Believe it or not, the ground in the unused harness is switched on and off with the lights. So youíll have to get your ground somewhere else. I used this bolt on the firewall near the switch cluster. Connect to your switchís ground terminal.
Test your switch operation in a non-traffic area at low speeds. Push the DEST button while driving. The Address & POI icons should be grayed out. Activate your cutoff switch and these icons should become active. Turn off your cutoff switch and they should be grayed out again.
It would probably work. You'd have to identify the speed sensor wire for that particular model. Each wiring harness is different.
There's another nav hack for the IS that's better than this one, where the speed sensor and display output circuits are disconnected from the nav unit but then spliced into the display unit's speed input. There is no switch required and it allows smooth map operation simultaneously with no speed lockouts.
Unfortunately, it doesn't work with our ES350. I identified the appropriate wires and made the changes, but no go. This manual hack is the best we can do until someone else comes up with something better.
Like I said, put it wherever it's convenient for you. The easiest and cheapest place to mount a button or other type of switch would be in the center section's left triangle trim piece by the driver's right knee. It would be easy to modify (since you can take it out and work on it), and it would be relatively cheap and easy to replace should you want to remove the switch in the future.
Another option: you could make a metal bracket that would attach somewhere under the dash but stick out from under it so you could mount a switch there. That way you would avoid cutting into the dash itself - a rather permanent choice.
You could wire it into the little drawer compartment to the left of the steering wheel. Either cut through the drawer to mount it outside, or mount it somewhere inside the storage area.
The possibilities are endless, especially if you use a small button.
I may never have the nerve to take on a project like this on my own ES350. However, I just want to thank you for the time and effort you put into this excellent presentation. Seeing it reminds me, that the reason I joined this site was to learn and share important and interesting information about our automobiles among and between intelligent adults.
Some of the nonsense in many of the threads lately have gotten so personal and childish, I was about to stop visiting Club Lexus. Thanks again for getting us back "on track" where we ought to be. Be Well.