South East wiring harness trouble.

My '14 Tacoma (4cyl 5 lug 2wd 5spd) did not come wired for a trailer. I installed my own Draw Tite, and purchased the "Southeast Toyota" version of the plug -n- play wiring kit, with connections to the battery, ground, and plug ins at the driver and passenger side tail light. There is a small black box (relay box?) that gets mounted in the driver tail light housing. Long story short, I hooked up to a trailer today (with LED lights) and got NOTHING, my neighbor (an electrician) came over and tested it, said everything looked okay on a multimeter, and I tested it with an incandescent bulb from my mower, worked great... Is this an LED thing? Anyone else using this same harness from SE Toyota without trouble? Any help would be appreciated, I have a call out to the dealership but have not gotten a call back yet.. Thanks for the help!