It's quite definitely not the same thing. I can't trespass on property I own. If I owned a substation, then it would be appropriate for it to warn "Danger! Risk

It's quite definitely not the same thing. I can't trespass on property I own. If I owned a substation, then it would be appropriate for it to warn "Danger! Risk of fatal electric shock!" but a "No trespassing" sign simply wouldn't apply to me and therefore provide no advice. As others have said here, it would be far safer to warn owners of these cars "Danger! Risk of fatal electric shock! No user serviceable parts! Service must be done by a qualified engineer." In fact without those warnings, I suspect that they would be legally liable, though IANAL, on the grounds that any reasonable person would know that "You must not open your own property" is not enforceable or reasonable, and when they do so, and die of electric shock, that is unexpected. "Risk of injury from moving parts" isn't going to put off anyone who has ever wrenched on a car, either.