Having the brake lights on the trailer come on in a breakaway is the least of
concerns.
The trailer brakes come on full power, locking the wheels, to slow the trailer
down as much as possible before it turns, rolls over, crosses the center and
hits the school bus. (:-((
No, the trailer brake lights don't come on if the breakaway is activated.
There will be no breakaways if the trailer is properly attached to the tow
vehicle, at least not unless the rig is in a big crash.
I have seen quite miserable chains even on new trailers. The chains should be
strong enough that the entire A-frame or tow vehicle rear frame is torn off
without breaking the safety chains. Heavy screw ("French") links rather than
open hooks should be used.
Al Grayson