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I have an Allison Transmission 545 and the speedometer wont work. its not the gauge that is broken that I know?
What makes the speedometer/odometer move? where is it located at or what does it look like?

5 days ago
See that is where im perplexed because its electrical not cable driven

I own a shop, and can tell you this, If it works from electronics, then you have what is called a VSS car speed sensor. they're typically installed in the rear housing of the transmission on the drivers side, or in the 4x4 unit on four wheel drive vehicles, and in some rare cases may be on the top of the rear end housing just above the ring gear. they are called a sensor, but in fact they're a generator, and they produce a tiny electrical charge by passing a reluctor wheel with teeth on it past a magnetic pick up. To test the sensor, unplug the harness, and attach a volt meter to it, and use the mili volt setting on the AC scale. With the ignition switch on, turn the drive shaft, and you may want to see the meter move. If it does not move, then reverse the hook ups from the meter, and attempt again. you may be able to test the speedometer by moving a part of metal back & forth real fast in front of the pick up, and it'll show a reading on the speedometer, if the pick up is good. The reason to test it with a meter is to insure you have the correct sensor. There are other sensors like the TCC Torque Converter Control sensor, but it's in the input shaft area of the transmission. Yours should be in the rear housing, 4x4 unit, or over the ring gear of the rear end.
Glad to help, Good luck.

Certified Master Mechanic, Shop Owner, 40 yrs. experience.

there are to gears in the transmission that drive it follow the cable down to the trans.