On the Ford F-350 the speed sense wire is found at the PCM (power conrol modual). The wire is grey with a black stripe. The PCM is located on the driver side of the firewall in the engine compartment. The only way to truely test this wire is to have a multimeter and know how to use it. Basically you have to have the wire hooked up to the multimeter and test for voltage, however you have to drive the vehicle and see if the voltage increases while you are driving. One way to do this is to connect a wire to the grey/black wire at the PCM and run it into the cab of the vehicle so you can test it w