XLT tail/brakelight Issue

Hi there I have a 1997 xlt Limited and I put a different tail light on it (more specifically off of a 2001 Polaris trailboss 325 atv) it had 3 wires so I assumed it had to be close to the same as the old one as it had 3 wires as well. I did have to switch all of the wires around on the old harness on the sled to make it light up at all. So without the lever being pressed one of the two filaments in the bulb is lit which seems right but the BRAKE indicator on the dash is lit up too. When I squeeze the lever the bulb still has only one filament lit but gets a little brighter like there is more power going to just that filament? And the brake indicator on the dash gets a little brighter too. So I guess the problem is that one filament isn?t doing anything and my brake indicator won?t shut off. It just confuses me why the indicator won?t shut off. The sensor seems to work because the lights get brighter? Is the different tail light messing it all up? I put a voltage tester on the wires and it won?t even read. If anyone has any info that would be great.
Thanks, Erik

XLT tail/brakelight Issue