Not sure about the in line reset. Maybe the easiest solution would be to mount a seven pin plug and use the corresponding male plug on each trailer. I have three tow vehicles and three trailers and have them all set up alike. It's just plug in and go. Also make sure you have a good ground on each one.
This is what I did, the one trailer does not have brakes so I just did not use those terminals.....I also wired a ground thru the plug, relying on the ball is asking for grounding issues.....
