ATS - Transfer switch location

I bought a transfer switch that was designed to piggy back on the rear side of the power converter. I installed it, and it did indeed slide onto some plastic rails built in the unit. I used it to transfer between inverter and shore power. I believe it was a WFCO converter and transfer switch. I had to unscrew the converter, pull it forward, in order to mount the transfer switch.

Also, I bought a little camera on a flexible line that plugs into the laptop for looking in the hidden areas to try to trace wiring and it helped solve some mysteries without disassembling anything.