The Hondas do not have a ground/neutral which will show a fault with a circuit checker. My trailer also has an internal Surge Guard but it is only on the Shore Power connection. The generator connection on the front of the trailer does not go through the surge protector which I understand is the way it should be. Logic I assume is that a generator is unlikely to spike enough to do damage. Just remember not to connect the Generator outlet to shore power.
Rich with the model you have it would logical that there is a remote indicator someplace in the trailer that will give you messages. Easy to install if you don't have one. If both circuits, shore and gen, are wired through the 40250 it sounds like it might have gone bad. Just looking at the Surge Guard site that model seems to have an automatic transfer switch built in. If you can see the unit there are display lights to tell you if it is getting power.
Optional 2-line plain English display (display p/n 40272 & cable p/n 40258) with continuous visual indication of source voltage (L1, L2), load current or diagnostics. LCD technology
Transfers to generator power automatically when energized after 30 second delay in generator mode. When both shore power and generator power are available, generator dominates after a 20-30 second delay. Once the generator is shut down, shore power activates after a 3-4 second delay.
Indicator lights on the front of the ATS indicate the presence of input power for L1 and L2.
All of this being said this might be a situation that without a valid ground/neutral that with a modified plug being used on the Honda's they won't work with the Surge Guard. Someplace I seem to remember that someone contacted them and they sent a diagram/photo of how to make a modified plug.
See this post and others like it: https://www.heartlandowners.org/arch...p/t-26375.html