Trailer Loght Wiring

I know this is not a motor problem but I have to replace the wiring on my trailer. I have the new wire secured to the old with the marker lights removed. When I tried to pull it through it will not budge, it feels like it is clamped down. It is a 02 Skeeter trailer. Any ideas on how to thread it through before I lose another day of fishing. Any help would be greatly appreciated. Thanks