"Intent" has some major part of the definition of your guilt and your intent has already been determined by your self-admission in your first post: you know the quad is not yours. The way I see it, your only choice is to call some authority and report the lost vehicle. If you are back there, put a plastic bag over the air intake hole to keep mice from moving in. If the authorities don't move the thing in say, 6 months, you might make a case that it is abandoned, and that your new intent is to strip an abandoned vehicle, as long as you can keep some proof of having reported it originally.
2016 Honda TRX420 AT EPS IRS Camo
Camo duck tape on warning labels