Last Sunday after I came back from Augusta with a non working cruise control I wondered if it was related to the non-working radio.
A search of the internet turned up a PDF of a 2003 Miata Wiring Diagram that I could use to help me trouble shoot my electronics woes Turns out that the radio and the cruise are related.
Attached is a segment of the cruise control wiring diagram and in the upper left hand side there is the Bose radio with a red/green wire connected to it at Pin I. This is the speed pulse coming from the PCM so that the radio knows to increase the volume as the car’s speed increases. It is also used by the cruise control module.
Even after seeing this tenuous connection I couldn’t believe that a dead radio could cause the demise of the cruise control, that is, until I replaced the head unit and the cruise started working again…