I have a '90 240 that keeps throwing the 3-1-1 code which is no speed signal to the ECU. Also, the cruise control doesn't work. Both the speed signal to the ECU and the cruise control come from the speedometer. The speedometer and odometer both work fine. Earlier this year, my sons were re-installing the instrument cluster and they didn't know where the red/white tach wire goes to (I don't have a tach). Anyway, they hooked it to the same connector as the yellow wire that goes to the cruise control unit.

Assuming that they must have fried something on the circuit board in the speedometer, I pulled a instrument cluster from the junkyard. However, the one I pulled was from a '91. Apparently the circuit boards were changed in '91.

The '91 speedometer doesn't work when installed in my '90. Does anyone know if the sending unit in the differential was changed as well? Also, does anyone have any ideas on how I could bench test the speedometer?