The wiring diagram in your owner's manual may be wrong.
 

While assisting Goodair with an electrical problem I discovered that the wiring diagram for my 2310H does not match the trailer wiring.

While tracing the primary 12 volt power to the master switch area I noticed the diagram, Drawing A, showed the master switch/lift switch area for the older model HiLo trailers that had the toggle switch and the red warning light. I don't know what model year last used that arrangement but it goes back at least ten years. Later model HiLo had the two rocker switch arrangement with no red light.

So, before you start checking your electrical system make sure you have the correct diagram. Refer to the diagrams in this link, they appear to be correct. They are easier to read as well.

https://www.hilotrailerforum.com/f51/...ry-wiring-116/