Thanks for the information. So far, I know the cable went straight from the tranny to the speedo when I disconnected it to diagnose the problem, but that doesn't mean the adapter wasn't bypassed in the past and it's still under the dash somewhere. I'll have to take a look for something I don't recognize. I suppose it's possible that someone in the past removed it because they thought it was the reason the speedo wasn't working and then just left it off when it didn't fix the problem. Or maybe it really went bad and was removed.
Is it possible that the adapter was never there? Or were these standard equipment on all trucks with a two-speed axle?
The two-speed axle on my truck is vacuum shifted, what would I look for as a possible connection to the speedometer adapter? Perhaps I could follow it to the location where the adapter is or used to be. I've clearly seen the vacuum switch bolted to the side of the tranny..in fact, I temporarily removed it when I changed out the clutch and had to remove the tranny.
