try unplugging them one by one and seeing what happens.I have a 2018 frontier I bought the t-1 connector kit from etrailer. My problem a year later now is my left brake light stays on all the time while the trailer is plugged up. It's just the plain flat 4 connector I have emailed etrailer it's been about a week now and they haven't answered with any possible solutions yet. I'm thinking it could be 1 of the 3 relays that comes in the kit but I don't know which one operates the brake lights? There are 2 blue relays, and 1 larger brown relay.
Yes as soon as I plug it in, or leave hooked up while the truck is turned off. The left/ drivers side brake light stays on until I unplug the trailer. I hooked it up the other day so as to have it ready for the next morning. Later that evening my neighbor called and ask if I knew I left my truck lights on. When I went out to check it was just the left trailer brake light on the rest including the truck where all off. It's definitely odd for sure it's been wired the same way for about a year now, and it never did this before.WJ, check all your trailer grounds. Are you saying that the left brake light comes on as soon as the trailer's connected, or trailer connected and engine on, or trailer connected and running lamps on?
Been wired the same way for almost a year now. I even tried it with our boat today, and it does the same thing.