Dearest Merlin,
I have been in the Automotive industry for many decades in all forms of roles, been working with ATVs for the same period.
Never ever have I come across this one seems the dealer is clutching at straws. Unless they are only telling you what you need to know and there is some critical issue they will not share with you…….hmmmm.
It’s an impossible scenario, i.e. a brake switch or a brake switch circuit causing a power loss, no no, start again bud.
Start with describing the symptom or fault but blank out the brake switch and the brake switch circuit.
The only way any circuit can cause a power loss or drop in engine performance is if that circuit shares the same path to Earth/ground as the petrol injection ECU. An extremely rare occurrence I must state, unless some gorilla has rewired your whole loom. Petrol Injection ECU’s tend to have dedicated earth/ground points and to my knowledge and experience do not share that same ground point with other circuits directly. However, one must not forget that the whole chassis/frame serves as and Earth return to the battery.
GMSAHFR