1985 300ZX Turbo with digital dash has a Cruise Control failure with the master switch light coming on but the set speed button on the driving wheel not working?
If you have a manual transmission the problem could be the
clutch petal. There is a switch on the petal that is activated when
you depress the clutch turning off the cruise control, the button
comes apart with age and will cause the switch not to activate. The
button can be purchased from a Nissan dealer for couple of dollars.
They are very easy to install, no tools are required. While you
there also check the brake light button they also fail. They are
the same part.