It will probably help you find the speedometer cable and its route through the firewall, it has to go through the body of the cab somewhere, by removing the instrument cluster first.
I am giving you an exploded diagram of the instrument cluster, it does not show cable hookup but may come in handy. I also am giving you an exterior diagram of the transmission showing parts #30&31, in top right box, as the speed sensor and the speedometer cable drive.
The service manual I have is somewhat ambigusous as the same tranmission is in the "S" series and is cable, but the "K" series alludes to the cable running from the tranmission to posssibly a hookup outside the cab that converts the signal there and sends an electronic signal to the instruments. I am really not sure about that as the wording in the service manual we sue can be very mis-leading. I just wanted to give you the information as I could best translate it. Without supporting diagrams showing the entire path of the speedometer cable I really cannot give you a definitive answer. I think between the diagrams AI am giving you and information, it should be easy to figure out how the setup works with the truck in front of you.
Let me know if there is anything else you need.
Images (click to enlarge)
Tuesday, May 15th, 2012 AT 6:06 PM