I've got a regular cab 2015 Silverado that I plow with. I recently purchased an Ultra-Tow mini light bar within the past week. I used to once, worked extremely well!
I took my plow & light bar off today to go get my truck washed. Put the plow & tailgate back on, along with the light bar. I tried the light bar, and wasn't getting anything. I looked at the plug & saw there was no light saying it we're on.
I went to Lowe's and grabbed some 5-amp fuses, and tried those in the plug. At first I still didn't get any power, but then I pushed the plug into the outlet with some more tension, held it there, and got power for a few seconds. Then the power cut out once again. At first I thought it we're the fuse's being blown, but looking at them not a single one looks fried.
I can maneuver plug around inside the outlet a little and the power comes and goes. Eventually I cannot get power unless I switch fuses.

No idea what is going on, but any help would be appreciated. Thank you!

Edit, here's the light bar that I'm using.
http://www.northerntool.com/shop/too...7142_200617142

 

Have you figured this out already? I would use voltage meter to see if there's a stable power on it. It could be tripping ground wire or something that shorts after the wash.