help with speedometer

Maybe a fuse got tripped along the way ?

 

I'm going to throw this out there just on the off chance that it might help. Is there any spots that the harness will flex when the truck is moving? I had a pickup truck with a voltmeter that would spike over 18 volts randomly. I was pulling my hair out over it, tested everything, ohmed out everything and could not find anything wrong. Turned out the ground cable had started to rot in the middle. It would make contact most of the time but would open up when the engine would torque up under load. The only reason I know it was rotten was because I sliced it open, there was no indication otherwise.

Another thing, although unlikely, is maybe the pins at the harness connectors are loose. It is very rare but I have run into that issue a couple of times.