Originally Posted by goshawks00
Some one else suggested it may have been a radio wire, sorry just don't know.
It would not be a radio antenna if that is what was meant. Putting an antenna between two aluminum panels would guarantee no reception. Or, the wire goes to an outside antenna. If the trailer has a radio, see if reception has been affected. If so, your electrical issues are easier, but you have to fix the antenna question.
If it is a wire for an option that was not installed it may
have 12 v. power to it at one end at the break. I don't know if you got both pieces out of the hole, but if either has power to it, it means it may short out something eventually. If it were for a back up light, that would assume the tow vehicle was in reverse and the trailer plug on the tow vehicle had a contact for reverse. Trailer plugs have changed since your trailer was built and your tow vehicle may not have a contact for reverse. If the trailer has a 7 way female plug, it probably has been modified from the original one. It may have a 4 way and that would plug into the separate 4 way on many modern trucks—usually used for small utility trailers. I believe there are 7 way plugs with a different pattern than contemporary ones, but if things worked beforehand, you probably don't have an older 7 way on the trailer.
A modern 7 way plug has a reverse wire—purple according to a diagram I found on the internet. You could check the contact on the plug for power. If none, good. The tow vehicle may not have a fuse installed for that wire, but it may. If it does, pull it out and make sure the tow vehicle still has back up lights. If the fuse only powers the plug, you solve a potential problem by removing it. The umbilical to the trailer may or may not have a wire for reverse and you would have to trace the wire and disconnect it and cap it where it ends, maybe at the trailer fuse panel. It may not be connected to anything and the color code may not be clear to you (or anyone). This may require removing each wire from the tow vehicle where they junction and seeing what each does (while truck is in reverse and the plug at the back of the truck is hot). You only need to test wires that are black and disappear in the walls—that is assuming the mysterious black wire is not attached to another wire of another color. You may find a wiring harness that comes from the trailer plug somewhere near the 12 v. panel—that would be good luck—and someone clipped off the reverse wire and it contracted into the harness and you can't see it (bad luck). Make sure there are the same number of wires at that end as at the trailer female plug that plugs into the truck.
One problem is that someone may have replaced wiring and not followed color codes. Normally black and red are hot, white is common (the other side of a two pronged plug), green or bare is ground. But there are other colors used when you have multiple things powered and some solid colors with a different color stripe running around them. Striped wires and different colors usually are found only on 12 v. circuits, not 120 v. Someone may only buy black wire (or another color) and you won't know that and codes may be useless. If you see a different color electrical tape wrapped around a wire, that means the tape indicates the actual color, not the wire.
If it were me, I'd want to know what the mysterious wire did (if anything) and eliminate any problems it may cause once messed with.
To quote Zippy the Pinhead, "are we having fun yet?"