I will be towing my truck behind my RV - it's a bus-type motor home. To take some of the braking responsibility off of the RV when stopping, a braking system was installed in my truck that activates the truck's brakes when the controller senses forward movement stopping. The braking system came with an indicator light that (when hooked up) I can see light up if the system activates the truck's brakes. It's a "nice to know - peace of mind" thing to know that the truck's brakes are working to help slow the whole thing down. In order to know if things are OK, the indicator light needs to work off of the brake pedal (therefore the brake switch) and not off of the brake lights. The way everything is wired, the brake lights are energized by the wiring from the RV, so I can't use the taillight wiring to connect it. I have been under the dash of the truck 4 different times looking for the switch and just cannot find it. Hope this helps to clear things up.