Speedo works part time

[Bigiron]

I've got a 93 D-250. Truck has 204000 miles any ideas why the speedo works part time. Put a new speed sensor on and did not take care of the problem. I can live with no speedometer but OD does not engage if it doesn't read speed. Any ideas how to rewire the OD on a toggle switch?

 

[AnonEd]

I've only a 92 manual (and a manual truck) and no idea how to toggle in an OD-engage switch, but I'll toss some ideas. If the speed sensor (a "distance sensor" on back of transmission in my book) didn't fix it I'd anticipate wiring first, SBEC last. If you have an extra body turn the speed sensor with an electric drill to check it...possible it is not making mechanical connection to the drive.
In the '92 FSM that distance sensor runs BK/LB to a ground (w/ water-in-fuel sensor, crank position, IAT, coolant temp, TPS and transmission thermal switch). The WT/OR wire runs through one connector to #47 on the SBEC and pin 6 on the left printed circuit board connector behind the gauges. Intermittent connection in that wire would cause erratic speedo and no OD?
FSM says the OD control switch, valve body solenoid, case connectors and related wiring can be checked w/test light or meter. "Switch and solenoid continuity should be checked whenever the transmission fails to shift into fourth". The cavity numbers on the SBEC for relevant wires are: 10, wire T6 20ga OR/WT overdrive lockout control; 37, T61 20 BK/OR overdrive lamp signal; 47, G7 20 OR/WT speed sensor pickup; and 55 T60 20 R/LG overdrive lockout solenoid.
Hope this is some help.

 

[Wayne M.]

I think you’re losing your signal. Perhaps a harness issue? I had a ‘92 automatic, and I recall that happening. I replaced the sensor at the transfer case, where the pinion would have went if it had a cable driven speedo.