*Write Up* Installing the Yellow Box Speedo Calibrator

[Scuba]

With the addition of over sized tires and lower gears in the differentials my speedometer had a 24% difference indicating 90MPH at an actual 70. Not acceptable. Follow along as I install the Yellow Box Speedometer Calibrator into my 99 2.7L 5Speed Tacoma.

I checked the Yellow Box instructions and checked the wiring diagram on the NCTTORA site which led me to my conclusion of how to wire it up.

First, pull the wiring harness out from the trans/transfer case. There's 5 connectors (which I don't know the exact names of) that need to be disconnected and pushed towards the front of the vehicle.

There is the VSS connector as well as the rear o2 sensor harness on the rear end of the transfercase
[img width=800 height=600]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0056.jpg[/img]
This is the rear o2 sensor plug, which bolts onto the Tcase somewhere in the above picture
[img width=800 height=600]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0057.jpg[/img]

Moving forward there is the Tcase position sensor (passenger side) (I'm 99% sure that's what this one is called) I have small hands so it wasn't hard to get in there, but you might have to have your kid do it if you've got fat hands.
[img width=600 height=800]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0058.jpg[/img]

Then there is the front o2 sensor harness (passenger side, bolts into the hole I'm pointing at.)
[img width=800 height=600]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0059.jpg[/img]

After that you can shove the harness over the top of the transmission to the drivers side and unplug the 5th and final plug of which I do not know the name
[img width=800 height=600]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0060.jpg[/img]

Once you have the harness in a good spot with enough room to work (and solder) you can pull the shielding and the electrical tape out of the way to reveal the 3 wires for the VSS. They are colored as follows : Red/black for POWER. Blue for GROUND and Green/Red for the SIGNAL WIRE.

For the power and ground wire you will want to strip (not cut) about a 1/2" of the shielding off of each. For the signal wire you will want to cut it and strip back a 1/2" of the shielding on each end. This picture may be a little hard to see but will give you an idea.
[img width=800 height=600]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0061.jpg[/img]

From there you will connect and solder the following wires.
Red/ black from the VSS gets connected to the Red wire from the yellow box.
Blue wire from VSS gets connected to the black wire from the yellow box.
The White wire from the Yellow Box gets connected to the VSS side of the Green wire.
The Gray wire from the yellow box gets connected to the ECM side of the Green wire.

Once you have them all connected solder them
[img width=800 height=600]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0063.jpg[/img]

Once your connections are soldered you can wrap them in electrical tape and shove the harness back into the plastic shielding. Reconnect all your sensors and run the wires where they need to be.
I chose to run the yellow box into the cab through the shifter boot hole. The actual yellow box unit will sit in the dead space under the center console

Kind of dirty
[img width=600 height=800]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0065.jpg[/img]

For size reference
[img width=800 height=600]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0066.jpg[/img]

Here are the switches you flip to change the settings
[img width=600 height=800]http://i11.photobucket.com/albums/a168/Sycosurfer150/Truck/Speedo%20Calibrator%20Install/DSCN0068.jpg[/img]

That's about it. From there you will want to follow these instructions to figure your speedometers percentage of error and then use the correction table to get a rough estimate of where to start off for the calibration step.

My calculations gave me a 21% difference and I ended up having a 24/24.5% difference. So leave the yellow box in an easy to reach spot so you can take a test ride and get it where it needs to be. I think it is suggested that each time you change the settings make sure you power down the vehicle.

I took a run on the highway and had to stop and change it a few times in order to get it perfect.

After that you can reinstall your shifter trim or what have you and live a happy life knowing your speedometer is freakin dead nuts accurate

I don't know which models have the same wiring scheme, but I'd venture to say all 95.5 Tacomas and all 96-02 4Runners will have the same wiring colors. If not refer to your vehicle wiring diagram or use the method in the yellow box instructions to figure out which is which

EDIT: Thanks Erich. Links fixed

[Scuba]

The links were broken, now they are fixed. Hope you enjoy.
Thanks Erich

[troyboy162]

anyone know if these will work with auto trans? im probably too cheap to buy one but im not sure they play well with autos from what ive read. i dont understand why it would be an issue unless shift points are based on speed.

[Scuba]

Shift points are based on RPM's not speed. You have a VSS ? You'll be fine

[Crinale]

my speedometer is based on rear diff ring gear speed... haha.. so i have no idea how to fix it

[corax]

Nice write-up - I think my VSS is a bit different, will it still work if I cut and solder that big single cable going to the back of the trasfer case


j/k, anyway I think the 5th plug on the driver side that you didn't know the name of is probably the reverse light switch

[corax]

my speedometer is based on rear diff ring gear speed... haha.. so i have no idea how to fix it

If you're talking about the little bit on the top of the center section, that's for the ABS - you're '91 probably uses a cable at the transfer case just like mine

[Crinale]

o really? i didnt think mine had abs... well is there anything wrong with leaving it dc-d? cuz my new 3rd doesnt have a hole for it..

sry scub, didnt mean to threadjack...

[DHC6twinotter]

My '90 has a speedo cable at the tail housing (no tcase in my case).

Scuba, nice write-up! I'll have to look into this once I get a newer 4Runner.

[troyboy162]

Shift points are based on RPM's not speed. You have a VSS ? You'll be fine

this is an awesome writeup. ive done alot of internet surfing and youve got the most complete install instructions anywhere. i learned that my truck (96 4runner with abs) does not have VSS. the ABS trucks ive read take the signal from the wheel sensors and feed that to the abs computer. the the abs computer interoperates that and spits out a signal that runs to the dash gauges and then to the ECU.