I just got finished replacing basically the whole cooling system and noticed that the speedo is stuck all the over at 120. Car on or off.
I did notice a plug just hanging and not connected to anything. Kind of hard to see, but it comes off a group of cables that also contain the 3 connections on the left side(looking at the truck) of the windshield fluid reservoir.

Anyone know what this is and if it had something to do with my speedo?

 

Was it connected before?

 

That's the thing...I'm not sure. I just know I didn't purposely disconnect it.
That's why I didn't really think about it until I noticed the speedo

 

So I hit the expressway and gunned it to what I think was about 50-60 and the speedo dropped to zero and then went to 40 and started working fine

 

If that happens again, turn the key off, hold the trip reset button down and turn the key on. Keep holding the trip reset until it says check in the odometer window. That should run the cluster through it's self test, which moves the needles all the way through their range and should get it back if it's just stuck over there from gravity.