Try driving a ground rod near the trailer or entend a wire from your homes grounging system to the trailer and read with a a.c. volt meter from the frame or body of the trailer to ground.If there is a hot wire with a high resistance ground you may be able to see it. In response to the provious post,i would think that a circuit breaker panel in a r.v. should be considered a sub-panel on an electrical system,that being said ,the neutral and ground MUST NOT BE BONDED. this if code. the ez way to test would be to use ohm meter accrss the ground and neutral blades of the plug,no connection should be seen on the meter.if a circuit is detected the first place that I would look at would be in the c.b. panel and see if it is correctly wired. This is just my opinion,I am NOT a electrician,but have a lot of years troubleshhoting electrical problems.again just my 2 cents worth.