Electric Brake Trailer controllers are great for those folks who have multiple cars to pull the same camper or those who loan their camper to family and want the best braking system.You will still need to run a positive wire from your battery to the trailer mounted controller. You cannot use the electric brake light to power the trailer mounted electric brake controller.

Why? Because the light wiring is undersize and will cause voltage drop to your brake magnets and brake lights. 2.5mm cable is common and OK for brake lights but not OK for electric brakes. Your electric brakes will be underpowered and only operate 50% of their capacity as well as being dangerous.

A 4mm cable should be drawn from your battery to your trailer plug pin #5. You may be able to use this spare cable as an accessory when camping to run small 12v appliances on all vehicles.