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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

This is the rear o2 sensor plug, which bolts onto the Tcase somewhere in the above picture


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.


Then there is the front o2 sensor harness (passenger side, bolts into the hole I'm pointing at.)


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


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.


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


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


For size reference


Here are the switches you flip to change the settings


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