[simplechamp]

When BrianG did his he used 2 equal value resistors, simulating the pot being centered, and from this he got the action at about 1/4 trigger pull (forward or reverse depending on your radio settings). If you played with the resistor values a bit you should be able to make it turn on with even less trigger pull (or more, but sounds like you want it to come on the instant you hit the brakes). Just make sure the total of the two resistors adds up to the resistance of the pot your are replacing and play around a bit. In effect you are using the two resistors to simulate a pot that is fixed at one position.

For example instead of using two 2.5k ohm resistors you could use a 4k ohm and a 1k ohm (won't be able to use these exact values, but you can get close). Both setups add up to 5k ohm to simulate the pot, but the equal setup will appear as centered, and the other setup will appear as moved further one way or the other. Again, just play around a bit and see what kind of response you can get.