There is a 3-way controller on my rig. One video display (now JVC), with two side cameras and one back-up camera. The 3 to 1 controller is a white plastic gizmo under the video head, with a 12v power input, three video in, one out.
HTH
Yankee Clipper
2014 Winnebago Sightseer 33C on Ford F53 6.8l V10
2014 Honda CRV 4 down toad/Roadmaster Falcon2 with EvenBrake
TireMinder TPMS,Tiger, the Little Big Man minidachshund,
Rosey the minidachshund resident Princess-in-Chief