'76 C30 Cruise Control Help...

[chaseman17]

Hi. I am in need of some assistance diagnosing the cruise control on my '76 C30. It has worked perfectly ... three times...in the short time I have owned it. That tells me that the issue is likely something simple???

It has the single button actuator on the turn signal post. Simple on / off only. No resume, accelerate, etc.

There is a switch down by the brake pedal that I believe is part of the cruise. It has a vacuum line to the switch. The switch makes a hissing sound when the brake is engaged and no hissing sound when the brake is not engaged. (that makes sense to me)

The vacuum hissing sound at the switch by the brake pedal does not happen all the time when the brake is applied, but I feel like it should...??

The vacuum lines show no signs of leaking.

If anyone can provide some insight on what they think and how to test, I would really appreciate it. The cruise is the only thing on this truck that doesn't work properly and I want to get it dialed in.

Thanks in advance!