Here the deal I was a 3x master tech for 30yrs dealers as well as race shops and independent repair,then owning my own shop, most techs suck when it comes down to having to do diagnostics on wiring etc, they can do simple stuff even dealer Techs aren’t great ,it’s why they have to have those tech lines unlike regular repair shops where we work on every brand and everything with a engine ,dealers get good at one thing maybe a handful if that’s all they have done ,if I was you I would call around to a shop that specializes in electrical repairs, back in the day I used to go to dealers and other shops after hrs and fix stuff they couldn’t before the internet etc…
If they can not figure it out in a couple days they aren’t ever going to it will sit and the tech will go back to it when he is bored or forced to do it ..
If you were paying cash they would be on it none stop but warranty work has a time/hr limit …
My guess is the harness it messed up if it has water in it but again I’m just guessing I’d go grab a few relays and some jumpers and make sure everything worked with direct current and slowly back track from each component until you find the common lack of contact be it power ground ,or lack of signal…
Good luck I know it’s not much but I hope it helps ,if I was around I’d come help ya …