Possible Causes

WARNING: This page is about a different car, the 2003 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.

Possible causes are:

Connector or terminal malfunction
Cruise control switch malfunction
Open circuit in Black wire between cruise control switch 8-pin harness connector terminal "C" and body ground
Open circuit in Black/Blue wire between cruise control switch 8-pin harness connector terminal "B" and PCM 104-pin harness connector terminal No. 15
PCM malfunction
Short to ground circuit in Red/Blue wire between cruise control switch 8-pin harness connector terminal "B" and PCM 104-pin harness connector terminal No. 15
Short to power circuit in Red/Blue wire between cruise control switch 8-pin harness connector terminal "B" and PCM 104-pin harness connector terminal No. 15