Cruise control diagnosis and fix

PGSS · Dec 14, 2019

philbquick said: ↑

I didn't read every response but here's everything I know about this system. The switch on the brake pedal has 2 switches inside. One switch is open (or off) when the pedal is up, it closes to turn the brake lights on. The other switch is closed (or on) when the pedal is up, this supplies 12 volts to the cruise control. When the brake pedal is pressed that switch opens and interrupts 12 volts to the cruise control which disengages it until it is re-engaged at the turn signal switch. There is also a vacuum purge valve on the brake pedal that is closed when the pedal is up. When the pedal is pressed the valve opens and it removes the vacuum from the cruise control which also dis-engages the system. When this valve leaks it can cause the cruise control to surge or not engage. When you press the brake the system dis-engages 2 ways, earlier systems didn't have the purge valve. With that said, you can trace the hose that goes to the valve a cap it off at the actuator under the hood for troubleshooting (you don't need it). You can test the turn signal lever switch with an ohm meter.

Hope this helps.
Click to expand...

A month late and not to highjack the thread, but is this the scary surge issue I most likely had in the day with my 73?

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Cruise control diagnosis and fix

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