On my 60 trdwnd ,the ground from the battery neg is in the trailers battery box ,originally mounted on the front of the trailer under the front window ,(as mine is) enters into the coach in the box area and thru the wall and goes into the inner wall down low on the curbside front ,near a double glass fuse assembly like older houses have .The ground does NOT go to that fuse panel ,I just referenced that for information .It screws to the wall thru an eyelet on the end of the wire .Now if your wiring has been changed or otherwise updated it all may be different .The ground wire for the trailer
never screwed to the hitch or the tongue .Thats always a crappy connection place ,corrosion sets up" house" very fast .you want the ground to be an extension of the ground at your trailer plug ,no grounds on the frame rail
just have a wired path from the trailer ground ,inside wall (metal ) and have
it go to the trailer battery ground ,then on to the trailer plug itself .
My 60 trdwnd is original in its layout and works just great .I even have the two umbilical trailer plug connections as original ,one is for 12 volt
negative only ,the other is for lighting and trailer brakes ,turn stop etc.Now then ,this may answer your question if the one plug (12v pos /neg ) has been
changed .there should be TWO plug sockets , one in the middle at the base
of the front of the trailer and the other towards the streetside ,outside of the tongue frame ,right by the bottom edge of the trailer front .so you would then find the original ground might be up in the belly pan where the
socket may have been .Anyway ,not certain whats been done but thats the story as how it originally would have been .Yes I do know that my original
setup of two plugs is not todays standardized way of doing it ,but If my trailers is to be towed, my International will be the only one to do it ,and my
trailer retains its original features .
Scott of scottanlily