Nitro's come with the solenoid. My 15' ZV18 had it and had a flat 5 plug in. Most new trucks can detect if there is a trailer plugged in. My Silverado can have different trailer profiles that you create for each of your trailers. I just completely rewired the trailer for my G3 Angler. I connected my Silverado and ran a electrical connection test. It ran through all the lights and the reverse lights. When the reverse lights came on I could hear the solenoid click on. Anyway, if you don't have that type of function you can just have a buddy hold the brake and put it in reverse and listen for the solenoid.
If it doesn't work then maybe you have a blown fuse in your truck. If that's the case check for a bare spot on the wire going to that solenoid.
So there we were, 4 against 40, they were the toughest 4 I've ever seen