This 1997 Chevrolet K1500 pick up came in with the speedometer, tach and shift indicator not working sometimes. In testing I also found that there were codes stored related to the TCC (Torque Convertor Clutch) and transmission. P0740, P0785 and P1860. This is a pretty common problem but I was looking for a quick simple test that almost anyone could do, to confirm the cause. The simple test is to check for ignition voltage at the “Trans” fuse, #20, 10 amp at the fuse box located at the left (driver’s) end of the dash. No power here with the key on and most likely the ignition switch is faulty.
This fuse is powered by a white wire from the ignition switch. Check there for power as well, with the key on. If power is not present, the only other test is for power on the red wire at terminal D5 of the ignition switch connector. It is easier to just confirm power on both red wires and not worry about terminal designations. For more information on getting to and changing the ignition switch please click here.