On my boat trailer (Ranger), the extra wire in the trailer plug is for a solenoid that releases the surge brake when you put the towing vehicle in reverse. If that is your case, you may have to get a 6 wire male plug and a 5 wire female plug and make up your own adaptor. Most 6 prong adpator set ups I've seen are 6 to 4. Have you checked Hopkinsmfg.com? They make Hoppy products and they may have it. Advance Auto Parts stores can usually order most anything from Hoppy that they don't have in stock.
'07 Country Coach Allure 470 Siskiyou Summit #31578, Cummins ISL 425; 2014 Ford F150 toad; Air Force One Toad Brake.
Glen Allen, VA; Smith Mountain Lake, VA.