Cruise and jakes not working.

Check your Brake Switch.

 

This. You'll have two switches, the normally closed one is the one for cruise/Jake. The NO switch is for the brake lights

 

That's how most trucks of that era were setup. I've seen some where it was all one switch (it would have 3 terminals) but I can't remember what truck that was.

 

Could also be something in the fuel pedal.

 

Throttle won't kill the cruise, though.

 

Brake switch wouldn't kill the jakes though either. When you give it fuel I think it overrides the cruise, I could be wrong. It could be set up where the jakes won't work with the cruise on.

 

I remembered a former neighbor of mine had a similar issue. He was told it was the Throttle Position Sensor. Well he replaced it and it solved the problem.

 

Yes, it will override it once you'll put more pedal than the cruise setting is calling for.

A lot of those E-models came programmed where the jakes wouldn't come on until you touched the brakes.