Disengagement of Cruise Control

[Karl Welhart]

I am having problems with the disengagement of my cruise control every time I hit a medium to hard bump in the road.  It seems to be something related to the brake light.  I have replaced the air brake light switch and did not resolve the problem.  At one point, by pressing hard on the air brake foot pedal several times, the problem went away.  However, it is has reoccurred and is again happening every time I hit a bump in the road.

Any ideas on what may be causing this problem?

[Edward Buker]

Karl,

J11 12 pin Mini Fit connector seems to be where the connections come in to cancel the cruise control. It looks like a classic loose connection problem or if you have a switch associated with the cruise cancellation on the brake pedal it could be misadjusted or possibly a switch with weak or bouncing contacts due to vibration. Unfortunately I do not know where the signal originates that cancels the cruise with the brake pedal. There are a number of ways that signal could be created, simplest of all would be a mechanical linked electrical contact switch tied to the brake pedal mechanism like in most cars. Here is some info and a schematic.

http://beaveramb.org/PDF/PDF%20Manuals/David%20Henery%202000%20Marquis/SmartWheel%20Troubleshooting%20Guide.pdf

You do have the option to engage the cruise and press on the resume button to raise engine RPM just a bit while sitting in place. Using that as a telltale for the cancelation issue you could start wiggling wire harnesses and check if there is a brake switch on the brake switch mechanism that is playing a role here either loose, defective, or misadjusted. When the engine rpm drops with what you are doing it should give you a good lead on where your problem is. The cancel button on the wheel could be weak but they seem pretty robust. You could also just tap moderately on the wheel itself with the RPM up simulating road vibration and see if that has an affect by dropping the RPM. Hope this helps, let us know.

Later Ed

[Karl Welhart]

Ed,

Thanks for the reply, but I do not have smart wheel.  Yes, I can use the cruise control when stationary to increase the idle speed.  I have replaced the brake switch on associated with my air foot valve (bus/truck style) pedal.  The problem appears to be in the air foot valve, and not the brake switch.

[Edward Buker]

Karl,

It seems like if you can still use the cruise to raise the RPM while sitting there, then you could tap around, tug some wires and plugs associated with your cruise system and see what is tripping it due to vibration. My hunt would start rapping the control box circuit board with a screwdriver handle (wherever that is) and sorting out what is used by the cruise control to cancel the cruise when the brake is applied. I'm not sure if it is a signal off of  the brake light switch or where in your system that feedback originates. I do not know exactly what you are dealing with but BCS or Alliance may.

Later Ed