Peterson V5411 4-Way Flat Tester - Professional Electrical Outlet Tester for Home & Office Safety Checks | Perfect for Electricians, DIY Projects & Household Maintenance

I recently bought a new to me, used vehicle, and my trailer's lights weren't working. I have had some problems with the trailer's lights in the past, so I rewired the lights. When I plugged it in to my vehicle, the lights still didn't work. This led me to believe that the problem was with my vehicle, so I bought this tester to test it. To my surprise, the tester indicates that my vehicle's trailer lights are working. So, I borrowed my dad's truck, hooked the trailer up to it, and tested the lights. Again, to my surprise, the trailer's lights work just fine. It appears that my rewiring of the trailer fixed it, yet the lights still don't work when hooked up to my vehicle even though this tester says they should.This tester proves that my vehicle's trailer lights get power because the blinkers, tail lights, and brake lights all responded properly when testing. However, I suspect that the lights on this tester work even when the voltage is lower than what's required to make the actual trailer lights work. So it's good for checking to see if you have power at all, but a good result doesn't actually guarantee that the trailer lights will work.I'm hoping that my vehicle just has an iffy ground connection or something, but I haven't had a chance to look at it yet.