What vehicle is this on ??? Not that it matters, but the wiring should go like this :

Power from accessory circuit to speed control switch should be the black wire on the speed control switch.

The brake pedal switch is wired between the speed control switch and the transducer (dark blue wire).

On the transducer side of the connector the remaining two wires (black and yellow with tracer) should go to transducer. Connector on speed control side for these two will have white with tracer (matches up to black wire) and yellow (matches up to yellow with tracer).

Sure sounds like it is all wired ok, and that the problem is the transducer. I think mopar made the most robust cruise control unit, and the EASIEST to add to any car !!! Well, certainly any mopar !! And yes, a transducer from the 80's even though it looks bigger, is same unit and wired the same . . . give yours a try.

Good luck

Cheers

Mark

PS - hope to see you at Kalispell show on 14th !!! Look for the purple satellite.