Dennis & Brenda- it works like this:
1. you activate cruise by pressing On/Off on the SmartWheel (SW); signal travels on a twisted pair from the pc board under the pad switches to the SWModule above & left of your front Vansco modules; SW Module sends signal to the Actia Speedometer gauge computer; Actia originates a J1939 multiplexed signal & outputs same on the J1939 twisted pair data buss to be read by the engine's ECM (Engine Compouter Module, Cummins), & Cruise is On but not yet set
2. you press Set on the SW, signal goes thru same devices/path as #1 above. ECM reads output speed sensor data from Allison tranny (which is boradcast on the J1939 buss for whatever/whomever to read), calculates vehicle speed based on rear axle gear ratio set in ECM memory, and adjusts fuel/air inputs to engine to maintain that speed.
The SmartWheel version we have does not have option to output J1939 data signals, so the Actia computer is involved to generate that signal.
Most likely problem is that either your Set or On/Off pad switch is inoperative; you can buy a new pad switch PC board from SW IIRC. Check this link
for troubleshooting tips on the SW. Contact SW here
Could be that the Actia computer is snafu'd, but the pad switches are moving parts and more likely the problem. Could be the ECM is snafu'd, but that's way unlikely.