The ground is the last thing that protects you from a fault in the wiring causing a shock. You do have an open ground but you also have a fault in the wiring that leaks voltage to the coach's chassis. If you had a goog ground it would pull the voltage down to zero and you wouldn't feel anything and perhaps trip the breaker if really bad.
So you have two problems to deal with: a fault in the wiring and an open ground.
David
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