I agree with CPA (Jim).
The goal is to have the brake activate if the trailer becomes disconnected, your hitch fails, or whatever.
If the brake activation cable is attached to the chain, or if the brake activation cable is longer than the chains, it probably wonít activate, and youíll get no trailer brakes from this emergency device.
Make sure it is attached to your tow vehicle and is slightly shorter than the chains. That way itíll try to lock up the trailer brakes in an emergency, assuming their adjusted adequately.