[mustang67408]

Originally Posted by imjin

Hi Mark,

I didn't end up using that schematic, rather I cheated and emailed Mustang67408 for the right wire to splice into. I've seen a few installs done where they mounted it up under the vehicle and tied into the sensor cable near the transfer case, but it's much easier to just solder it inline with the speedo sensor cable attached to your gauge cluster. We'd need to find the correct cable that's specific to your 2004 model to splice into. The green & yellow wires from the Truspeed splice into your speedo cable, then the red is a hot 12v and the black goes to a good ground. I know the wiring harness on my 2001 looks a lot different than the later models. Basically, you cut your sensor wire, then solder the yellow Truspeed wire to one end of the cut, followed by soldering the green Truspeed wire to the other end of the cut.

From using it these last couple of months, I'm fairly certain that it not only corrects the speedo, but also the odometer, trip meters and gets the transmission back to where it was shifting in the right spots again. All the device is basically doing is allowing the factory speed signal to pass through it, where it adds to or takes away from the signal that reaches the ECU, based on the calibration screws you set for your particular setup. It's not really adjusting anything other than the speed signal, but that speed signal is the starting point for things to get out of whack with larger tires and/or different gearing from the factory setup.

Prior to the install, my tranny would always seem like it was staying in the lower gears longer than it used to (before larger tires were installed). After the install, I could tell immediately (from the seat of your pants gauge) that it was shifting differently, more like it used to prior to larger tires.

EXACTLY