Tow Brakes When Applying The Brakes When Towing A Travel Trailer The Sender Reads O.L Where Should I Start Looking?

When applying the brakes when towing a travel trailer the sender reads O.L where should i start looking? - tow brakes

OL media overload, overloading the circuit is established, such as cable or rusty brake magnets, visually the towing cables and brake, and remove the wheels and brake drums and look for worn or broken.