Boat trailer wiring help please

[JBinUTAH]

You can try running a wire from the fourth hole and test it that way, but make sure its a solid ground to the trailer. Otherwise you may have to ground each light with a seperate wire back to the ground on the plug or to the trailer itself. I tend to do it the hard way and ground each light with a seperate wire to the trailer and ground the wire out of the fourth hoile as well. Too many times it just doesn't last and I only want to do it once.
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