ECM Input Code EI79 - Cruise Control Enable On/Off Input: Notes
WARNING: This page is about a different car, the 1988 Cadillac Seville and 1988 Cadillac Eldorado. However, it is still accessible from the selected car via links, so may be relevant.
The cruise control enable switch provides power to the cruise enable input of the ECM. The ECM cannot allow cruise control operation until the enable or instrument panel switch is turned to the "ON" position, which passes 12 volts to ECM pin "C12".