Check Trailer Wiring

[Diana8638]

I've towed my horse trailer with a 2003 Silverado, 2007 Silverado and 2011 Silverado with no issues.  I purchased a 2015 GMC Sierra Denali and suddenly was receiving Check Trailer Wiring error messages, WITH dinging bells, over and over and over and over.   Had trailer wiring checked, electrician said trailer was wired correctly the problem was 2015 wiring.  Few months later, I acquired a 2015 Silverado.  Same thing, Check Trailer Wiring, with dinging, over and over.  Sometimes you go miles with nothing.  Sometimes it starts when you pull out of the drive way.  This does not happen when I use the smaller flat plug for my flat bed trailer.  Only when using the larger round plug.  Took to local mechanic and they could find nothing wrong with trailer or truck wiring.  They thought it only happened when brakes were applied, but this is not true.  They finally said they could not resolve the issue.  The trailer then went to a trailer dealership, that sales the brand of trailer I have.  Their initial checks on diagnostics showed no errors.  I left, the dinging started, I went back.  They rewired the trailer, replaced the brake box and have no idea what else to do.  Picked up trailer today.  Dinging took awhile, but eventually did start.  They asked if I had the truck rewired by the dealership - no.  Nothing.  It's happening on two 2015 GM trucks.  But has never happened in the 13 years I've owned the trailer.  Help?

[silveradosid]

check the break away battery, make sure it has clean connections and 12 volts