content: Our company had some trailers that had dead batteries in the 'break-away' systems. Instead of just replacing batteries - (which were quite expensive) I decided to replace the whole system. Found the 'Hopkins Engager' at Amazon. It was cheaper than a battery for our existing systems and came with a switch and everything else new. It was easy to install and it works good. I really like the battery meter that tells if your charge circuit is working on the pull vehicle. Good product