by Philip » Sat Aug 09, 2014 5:40 am
The PCM does not supply voltage for the speedo. It receives the same signal from the VSS that the speedo head does. The PCM then uses that signal for CC and OD usage. Your problem is before the PCM. Check wiring and connections first. Check for voltage at the VSS plug. Check the wiring back up to the speedo head with a meter to determine if you have a problem in the wire. The VSS input to the PCM is threw pin #7.
93 W350 Club/cab w/duals, buckets & console, B&W flatbed, G56, 6 spd, 3:07 rears, gages, HX40/16, 4" exhaust, 6X.018 sticks, rear air ride suspension