I have a 2013 378 and had a similar issue when unit was about a year old. I was popping breaker to outlet after extending or while extending slide. I found wires chafed in the bend where it goes up through the floor slide. I accessed the junction box as bubbles mentioned and ran a new wire. Iíve not had issue with since. As a side note I will mention had issue with bedroom slide also. There is wiring and junction box under the floor of storage area under the bed. My wife put a couple cases of water under bed which in turn apparently caused the platform floor to slightly bow. When running slide out the bowed platform drug across the junction box located under there and ripped the wires. Installed a shallow gang junction box when rewired to allow more clearance. Be cautious how much weight is stored under bed until the junction box is replaced with a shallow one. If the platform sags and catches the junction box you will have another surprise under there also.
2013 Georgetown 378 XL