Trailer wire grounding issue

[Thegreencantina]

Hi. The right trailer tail/marker and side marker light have no juice going to them. I found there was current rear of the fender light, so I assume there's a break between the fender and the tail light. The wires run inside the frame so I can't check the whole black wire. I do have brake/turn on that fixture. Anyhoo.

I ordered a five pin harness (have the electric reverse release) but when I went outside to install today I found that my trailer wiring had full length grounds on each side. The connector plug actually has three grounds coming out of it: One ground hooked to the frame where it splits, and then one running down each side of the wishbone bonded with the two other wires. Unfortunately the wire I ordered only has the ground to the frame by the hitch and then two wires running the length.

I honestly didn't think of it at the time I was troubleshooting the light, so I went out to check. Sure enough there are three wires to the rear on both sides. My question, however, is this:

On each of the on lights on each side, instead of being wired directly to the dedicated ground from the front, the wires are spliced near the lights and ALSO wired to frame mounted grounds at each light (tail light assembly and side marker lamp)...

I checked the lights at the fender, which also have two pin connectors. It is spliced only to the black wire in the group and then grounded to the frame as well. The front side marker only has one wire going to it, so it's a non issue on that one.

Why would you (and will it cause problems) have a dedicated ground and splice into it to also ground to the frame? What do you think? Should I just run the new wire I have and hope the frame grounds at each light last?

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[Thegreencantina]

I was right, there was a break in the wire. Could this have been caused by having it grounded to the tow vehicle and grounded to the trailer frame at the same time? Sorry, obviously I'm not endowed with the electricity comprehension gene....

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[mactlman]

i would get a new wire kit and install if trailer is older--wires look crusty in pics---never use scotch locks either just asking for green corrosion

[Thegreencantina]

Good to know. Was thinking about them. I think I'm just going to use standard heat shrink butt connectors followed by heat shrink. I have a new wire kit, it just doesn't have the full length ground wires. I pulled them through to try and get through the weekend, but I'm planning on getting the wiring kit with the full length ground on either side. I'm still unsure about how the rear lights are hooked both to the white ground from the harness and also the frame. I've heard the term "double ground" but have no idea what it is or if it's a good or bad thing.

[billnorman1]

Sawyer picture of the bad wire. Unfortunately I have actually had some wires go bad lately, that should never happen but it does. The wire insulation gets porous and water gets inside and rots the wire.
Anyhoo you can't have too many grounds. The frame of the trailer should be at ground potential but sometimes it's hard to make a "good ground" due to paint or corrosion. If you rewire, don't worry about running more than one ground (white) wire, but for sure make it a good ground. You can run as many grounds as you feel like. Make solid connections with your crimper, grind the frame down to bare metal and use a lock washer under the ground terminal then paint over everything.
Introduce yourself to "Liquid Electrical Tape" from Harbor Fright. Paint it over the ends of your splices, be generous, then heat shrink over it while it's still wet to make a water and airtight connection. It's great stuff.
There are also some cheap cast iron crimpers at Harbor Fright that make a passable crimp. The stamped steel ones from WallyWorld are junk. Test every splice you make, if you can pull it apart with reasonable power you need to improve your technique.

[Thegreencantina]

Awesome! Thanks so much for the detailed explanation. Now to just lay out in the heat and get it done. Cheers!