I installed the GJ 3rd brake light, and I have to say while it's machined well, I am incredibly disappointed by it. The included wiring seemed super half baked (vampire taps? seriously?) and I ended up building my own harness for the thing, and then it took me an hour to mount it because of the awful hardware they include. Tinnerman clips are made to be used with sheet metal screws, not machined threads, and they don't even sit well because of the flanged edge on the truck. I'm probably just going to sell it and get the BPD antenna mount.
I had the exact same issues. Was very disappointed about the wire taps and refused to use them. Ended up making my own harness as well using JST connectors which requires cutting the stock truck harness. Not a huge deal as this is just a pigtail (part # ml3v-15425-ze) that plugs into the chassis harness and can be replaced if I ever wanted to delete the GJ light.
I reached out to the guy who makes the harnesses for GJ, who responded within hours, and he said the connector that would make that portion of the harness plug-n-play is on back order with a 2 yr lead time.
Before I knew that I ignorantly placed an order with GJ for their “factory wire harness”. After attempting to reach them by phone, email, website for weeks with zero response I cancelled my order on their site. After waiting another week or so with no response and no refund I disputed it with PayPal and GJ refunded me within a day or so. Terrible customer service and kind of don’t want to use their light, but it’s already installed now and at the end of the day it’s just a housing with BD lights and a harness made from a solid dude.
As for the hardware I ended up cutting the tinnerman clips in half as they don’t interface well with that flange. I then used some VHB tape and turned them into bonded nutplates that sit flat and won’t damage the body.