My slide has two outlets and they were installed using sj black 14ga cord. They run from a junction box on the frame, out to the boxes with over three feet of additional line. The then have two long, low tension springs, criss crossing across the slide, so when the slide retract at closing, the excess slack in the line is pulled up tight with those springs.
Works well, just inspect those connections to the springs periodically to ensure their not dragging or getting caught up in the wheels.
Bob and Better Half
2007 F-250 PSD, SW, CC, LB, 2WD
2006 TF32SS Cross Terrain Toy Hauler (sold)
Reese 16k slider