Just like towing a small Travel or Utility Trailer with electric brakes, the dolly "should" have a flat 5 pin plug. The wires are left turn/brake, right turn/brake, parking lights, ground, and brake feed.
Do you really think the dolly will have a 7 Pin connector?
Pigtail connectors/adapters to join the round 7 pin to the flat 5 pin are inexpensive and available at most RV supply stores and even Wal*Mart. And, if you want to add add'l lighting, there are splitters made for this purpose.
Like this: http://www.realtruck.com/anzo-traile...ing-splitters/
Now - if your dolly has some other plug set-up, you will have to do some creative connecting to make the dolly play with your RV and make the add'l lights work. It's not hard if you just know what wire goes where.
See here for more info on trailer wiring with 4, 5, 6, and 7 wire set-ups.
Trailer Wiring Diagrams | etrailer.com
Best of luck
Kim and Steve, Mustang LCDR (Ret), '07 Damon Outlaw #1193
I have seen gross intolerance shown in support of tolerance, Samuel Coleridge
WE LOVE OUR OUTLAW RV