1989 S-10, 2.5L, Speedo only works some times, and when it is NOT working the truck idles rough and the A/C does not work (as if the Clutch is not engaging.) But 5, 10, 30 miles and the speedo begins working, and all else works too???? Started very intermittently, got worse, and now does it every time I start the truck. DRIVES ME CRAZY!