This weekend a buddy and I "attempted" to hook up his third tail/brake light on his Kimpex seat on his 2010 sportsman 500. I had previously done one on my 2005 Sportsman a few years back and everything went smoothly, but it appears that the wiring has changed since then. I searched for a schematic but had no luck. Both bikes have three wires to the tail lights but they work all together differently. My 05 has one for tail lights one for brake and a ground with the brake wire hot only with the brake applied, the 2010 also has three wires BUT two are hot, and when the brake is applied one loses power.
We tried every possible combination of switching wires, verified that all lights (both on the bike and the seat) worked as they should but could not make them work together. We either got a really dim light or brake light all the time.
Any thoughts on what may be the problem?

 

Sounds like a normally closed circuit? You may need a relay. I tried to find a wiring diagram for you as well...a hard find indeed.