Sounds like something is getting wet that should not and is grounding out somewhere. Could be a simple control wire bringing the 12v to ground on a loose plug or something.
Try starting with the throttle, following that wire, up the handlebar and all the way back basically to the battery / controller, checking any canon plugs, wire plugs, any connectors, give them a good wiggle and press to make sure they are tight. If they are the rubber boot type etc, that looks like it's trying to be water proof, might want to open them up first, make sure they are not holding water under the boot or anything, then re plugging them back in nice and tight and making sure the rubber boot if there is one, is snug how it belongs on that connection.
Scenario: A bit of water is bringing the signal to ground. This is throwing the throttle faults, and since the voltage is maybe a small amount of volts low, because of the ground, it's throwing the power supply fault too. It could have high enough impedance that it's not blowing any fuses, but just enough to drag the voltage down on that very small gauge wire.
Aaron