The electric tongue jack I bought has one black wire with an in line breaker. The instructions say that the washers and split washers under the bolt provide the connection to the chassis.
I have two wires capped and stowed by the batteries labelled "Provision, Electric tongue jack", a red wire and a white wire. I took the battery covers off, the left hand one has a big red wire on the +ve terminal, there is a black jumper from the -ve terminal to the +ve terminal on the right hand battery, and there is a thick white wire on the -ve terminal of the second battery. The two big wires go into a plastic conduit, and the two smaller gauge wires for the tongue jack come out of the same plastic conduit, the conduit disappears under the chassis, presumably to the power distribution box. None of the fuses are labelled for a tongue jack.
Is there a way to tell which of the two big wires is grounded to the chassis somewhere? Motor vehicle convention seems to be -ve to chassis, are trailers the same?