Its weird to me at least

I drive my truck every day 1 - 2 hours (depending on traffic) to work and have had no issue. I changed my alternator about 2 months ago due to low voltage, just trying to be proactive.

I hooked up my new travel trailer this weekend to go from MD to Pittsfield MA to go camping. On the way up, all my gauges and radio went dead. I looked at the scan gauge and the Volts were 16.5 it would track back down to 13.6 - 14.5 and the gauges and radio would come back on. It ran up and down for the rest of the drive, the lights would also brighten when the volts were up.

Truck started fine when I stopped for fuel and the next morning. Coming back home on Sunday, it never happened once, or driving to work the last two days.

My thoughts are
1) regulator is bad, but why only when the trailer was connected...
2) trailer batteries were charged already on the way up and somehow were transferring the power back? On the way home, we had been dry camping, the batteries were low and needed the charge, so no "overload"

What can I check on the trailer or truck to eliminate one of them? Can the trailer, back feed the truck somehow? It is a new 2015 and is still under warrenty, so if I need to take it in, cost me nothing, but I want to at least sound like I know what I'm talking about

Any questions or help appreciated.

 

The "A circuit" voltage sense wire is corroded or has a break in it.

Splice a new wire from the connector and loop it back onto the charge post of the alternator.

Josh