I have a 99 Ranger 4x4 with 5 speed manual had to replace the 4x4 shift module to get the 4wd working and now the speedometer goes up to 90 just driving down the driveway. The module I bought was used because ford no longer makes them it had all the same numbers on it that the one in the truck had, I have now bought another used one thinking maybe it was the module bad but it does the same thing. 4x4 works great but the odometer numbers look like a gas pump the miles are turning over so fast. Anybody else had this problem I would appreciate any advice.

 

Welcome to the forum


In 1999 the 4x4 shift module is just 2 relays in a box, so nothing to do with speedometer.

The GEM(generic electronic module) is what controls the 4WD system and it also controls speedometer.
GEM is behind the radio usually on drivers side.
VSS(vehicle speed sensor) wires run from rear axle to the GEM, then GEM corrects for tire size and sends out "true speed" signal to speedometer, computer, Cruise and GEM(GEM uses corrected signal for 4WD, 0MPH to shift to 4low

IF you have 4 wheel ABS then the 4WABS module does the "true speed" conversion, not the GEM.

In any case what you are seeing is rear axle tone wheel speed, raw signal from VSS, which is about 30,000ppm(pulse per mile), speedometer is calibrated for 8,000ppm, so it would peg out pretty fast.

If you don't have 4wheel ABS then unhook the battery for 5 minutes and then reconnect, that will reboot GEM, see if it is now calibrating speed signal.
If not then you will have to have a look at the GEM wiring, but most likely internal issue.

4WD wiring diagram here