Speedometer Question

[Quackaddict]

OK school me up on this. I finally got to drive my truck yesterday for the first time ever. Look down and notice the Speedometer isn't working. I know a little about a lot of things but have never given a speedo a second thought.

It is a 1980 K5 has cruise.

Just trying to get someone to give me an idea of where to start as I am clueless on this. I have a haynes but not sure exactly where to look. I don't think I have VSS as old as it is but could it be a vacuum thing?

Someone please point me in the right direction

 

[Metrodps]

Speedometers on old style trucks and cars run off a small metal cable. They connect into the transmission and to the back of the speedometer. On a 1979 there is a piece that the cable goes into for the cruise and then to the back of the speedo. On yours I am not sure if it has the little box.

On the 1979 it was on the drivers side inner fender and had a cable that ran to the carb to control the throttle. Maybe someone with an 80 and cruise can help.