The "third" brake light (mounted on the cab) of my '97 F-150 is not working. Also the cruise is not working either. Checked the fuse for the brake lights and its fine, what now? Are the two problems connected?

This may be a stuipid question but is the bulb OK?. Do your tail lites work?. If they do then check for power in the cab lite connection. I know Mercedes is wired in this manner where if ta brake lamp doesn't work, it knocks out all kinds of stuff.

Yes, the taillights and other brake lights work and the bulb is not burnt out...I will try your suggestion however.