Speedo indicating bout 2X actual. Estimate pegs @ 40-45 mph. Operates smoothly and returns to 0 when stopping. Electronic unit. Same in Hi or Lo range. From info: speedo gets signal from VRM sensor @ end. of tranny - found it. From 2-speed axle control info: speedometer adapter in play in low range. Info reads like this is for mech speedo and a relay actually moves some gears driving a cable. Anyone know how electronic speedo gets range adjustment. Can't find the speedometer adapter shown.
Thinking that in 1987 there were no electronic speedos in trucks? Could be wrong. Yes, there should be a unit that shifts with the two speed to keep the speedo correct. If installing an electronic speedo I would think you would have to put the sender onto the end of that little gear unit. There may be electronic speedos for two speed trucks, I've never seen one....
F800 Speedo Adapter Think Ford started this in 1987. Shop manual has procedure for checking speedo but it doesn't mention the adapter. Schematic shows 4 wires to speedo: 1-power from ignition sw, 2-VRM signal, 3- ground, 4- backlight.
What transmission do you have? On my 1987 F800 I sold, it had a RT6610 Road Ranger. It used a manual cable to run the gauge. Pete