No cruise Control?

My 88 c2500 5.7 cruise control doesnt work, the fuse is good, replaced electrical box on firewall that connects to TBI( i beleive thats the servo ?) but that didnt help anyhow, what is the most likely culpret here, the multifunction switch or am i missing something easy?

It is most likely the switch in the turn signal arm. They are a slight pain to change out due to the wires routing through the steering column. The turn signal arm just pulls out but the cruise wiring must be fished in. I disassemble the steering wheel and turn signal switch and put them in, you might want to tie a piece of fishing line to the plug in end before pulling it out, you might get it back in that way if you've got plenty of patiance, I couldn't. The job shouldn't take more than an hour if it has to be disassembled. I think these arms are now available at Autozone and Advance for ~35 to 40 bucks.

Another area to check is the brake pedal switch. My '88 W/D shows a brown & light blue at the switch. Check for no continuity on those wires with the brake pedal released.

A wiring diagram and multimeter would really help. Unplug the connector from the cruise module and stick the positive lead in the hole corresponding to the main power wire, which comes from the on/off switch for the cruise. If there is no current when switched on, this is the problem. You may either replace the turn signal stalk, or run a wire from a circuit that is always on to the main power lead on the cruise module (that's what I did).

Also, there are two switches to shut the cruise off when pressing the brake or the clutch. They are located under the dash. When the brake and clutch pedal are not pressed, they rest against a button that only supplies power to the cruise module when it is pressed. A simple way to see if that is the problem is to press them in completely (sometimes the brake and clutch don't do this when they wear out) and see if you get 12 volts at the corresponding terminal on the connector to the module. I had this problem develop after gettting a clutch done. For whatever reason, the pedal didn't rest against the switch enough to create a connection, and the cruise didn't work. The right thing to do is get a new switch. The easy thing to do is cut the wires, and bypass the switch, which is what I did. That was naughty, but it worked.