I am customizing my Enclosed Cargo Trailer/Plane Hauler; I think I know the answer, just looking for confirmation; presently, the Running Lights, Tails Lights, Marker Lights, etc, run off the Vehicle Pulling the Trailer via the 4 wire Vehicle/Trailer Plug, and these lights are all grounded through the metal frame of the Trailer; I want to install a separate stand alone 12 volt system that is independant of the towing vehicle, will have its own battery, on board charger, etc; to power Trailer Interior Lights, Chargers, etc; can I ground these to the trailer Frame if I ground this Independant battery to the Metal frame as well, or do I have to run a ground right back to the battery and not ground the battery to the Frame?

Thanks.

Technically you could use the trailer as ground, I wouldn't.
In my opinion you will get much better connections by running
a separate ground for the stand alone system and eliminate
many future problems associated with bad connections.

Hope this helps,
KW_Counter

Yes you can use the frme as a ground nothing unsafe about it....the only problem with grounds is not to ground AC and DC together on the same ground stud... seperate them by at least 6 inches

JM05,
I don't understand the reasoning for this. Could you explain?

I'm the original poster and I'm curious as well what JM05 meant; in my original post I wanted to find out if the Trailer Frame Ground for the Signal/Running Lights Powered by the Tow Vehicle be shared with the stand alone separate Trailer 12 Volt System?

My thought was that there would be a conflict between the Two 12 Volt DC systems, I now realize no problem, a ground is a ground, shared or not shared; unlike AC where in simple terms, the Neutral needs to go back to the source; DC no Neutral just a ground.

OK I didn't mean to confuse anyone...A ground is a return path to the source.....so your running lights grounded to the trailer frame, powered by the car/truck will not work until the trailer is hooked up to the hitch...completing the circuit back to the source which is the car/truck.....now your trailer dome lights hooked to the frame is ok as long as there is a complete path...from the battery to a fuse, to a switch, to the light, back to the battery through ground. so the negative lead on the trailer battery needs to be grounded to the frame. as well as the return wire from the light.
I have seen numeriuous times on aircraft where AC grounded with DC causes problems...but You don't have that problem as you're only dealing with DC