King Control: KC 2600 Throttle System Diagnostic Chart

King Control (cruise control and throttle control) circuit board has a connection to the rear brake light circuit for two purposes.   

1) If cruise control is active and the brake light comes on, cruise control turns off, only to come back on with a new “set” or “resume”.

2) If the throttle control circuit does not see a ground connection through a brake light bulb, the coach will only accelerate to about 10 mph no matter how hard the throttle pedal is pressed. Burned out brake light bulbs will cause this situation. And a missing wire connection to brake lights will also cause this problem. King wants to know it can sense brake lights, so it can turn cruise off when brake lights will come on. If King does not see the ground, it assumes brake light wire is missing.  

Pressing the air brake pedal puts air pressure to brake switches, turning on brake lights.  

When the transmission retarder joystick is added, a relay is added just to turn on Foretravel brake lights. Allison does not require this relay to activate the retarder from the joystick.  

When the retarder is activated by using the brake pedal, brake lights turn on from air pressure switches.  

If someone adds a joystick and does not add the relay, joystick retard will not turn on brake lights. And if driving on a highway with cruise control on and joystick in a retard position, and the coach goes down a dip, the accelerator goes to zero position, retard comes on, and when the coach reaches the bottom of the dip, the coach will again accelerate and retard will go off.  

If the relay is in place because the joystick was originally part of the coach or the relay added, every retard action will turn on brake lights and immediately turn off the cruise, which stays off and must be reactivated manually.  

One can have a dash switch on the new relay control wire to choose between having brake lights come on with joystick retard, or not come on.

Here is the Foretravel wiring diagram for the add-on retarder relay located near the brake light air switches.  When this relay is closed, it turns on the brake lights.

This add-on relay is triggered by the retarder relay on the main circuit breaker panel by the front door.

The Bosch relay mounted beside and outboard of the two Brake Light switches on the forward bulkhead is the added relay that Barry Levitt speaks of.

Pull that relay and check for high resistance/clean and lube? I’ve found “not-ideal, resistance (10’s to 100’s of ohms of resistance), should be a dead short when the relay is energized”. I’ve replaced mine twice. It is not a friendly home for this component and therefore needs to pamper a bit.  

On my ’96 U295, the control is an aluminum box under the bed in the forward, passenger side corner in the engine room. Made by King Controls. 

On my 95 the cruise is Bendix, I have separate cruise and air throttle. If cruise quits I still have throttled. On some, if King Control quits you have no throttle.