Trailer lights conundrum

[HRemington]

Last summer my trailer lights weren't functioning.  Found I had a bad ground connection and a blown 20A fuse in my Honda Pilot tow vehicle.  Fixed all that and everybody seemed happy.  Coming back from a vacation trip last week, saw lights weren't on.  Found my trailer brake lights worked, turn signals worked, but no taillights or fender lights at all. Ground connection good, but found the same 20A fuse blown. Swapped out fuse and as soon as I plugged trailer wiring connector in, fuse blew instantly.  Disconnected trailer from tow vehicle, connected trailer wiring directly to a battery, and all lights worked perfectly fine.  So why does the fuse keep blowing?  Where do I look next? Doesn't seem like circuit should be overloaded with trailer having LEDs.  

Thanks for any ideas.  

[Bozboat]

One of your positive trailer wires is worn bare and shorting against the frame or a ground wire.   I would look carefully at the ground wire connection. My thinking is your grounding or shorting to the truck thru the trailer ball and not thru the wiring harness.

Edited July 29, 2023 by Bozboat

[dlb]

From experience:   Follow the positive wires to find the short.  Look for points where the wires go through the frame or metal guides where they may be under tension or pulled when you plug in to the vehicle.  The wear spot may be small but it will cause the short.  

[HRemington]

Thanks guys and I'll keep searching.  After the fuse immediately blew as I mentioned above, I did get more fuses just to try one more time.  This time the fuse has not blown yet and all lights working for now.  I still believe I probably have a problem as Boz and dlb suggest.  So if four wires and white is my ground, which color(s) do I follow?  What does it indicate that only the 20 blows, but the two 7.5s do not and that brakes and turn signals work while taillights do not?  If white is ground, yellow left turn/brake light, green right turn/brake light, then is only the brown wire my culprit? 

Edited August 1, 2023 by HRemington
added question re wire color

[justgary]

2 hours ago, HRemington said:

is only the brown wire my culprit? 

Yes, if the running lights are the only problem.

[HRemington]

On 7/30/2023 at 6:43 PM, dlb said:

From experience:   Follow the positive wires to find the short.  Look for points where the wires go through the frame or metal guides where they may be under tension or pulled when you plug in to the vehicle.  The wear spot may be small but it will cause the short.  

This was indeed it exactly, just as boz and gary also said.  I found the spot where the brown and yellow first go into the left side of the frame.  Sharp edge and a bare spot worn through on the brown wire.  I guess just tape it up, maybe with liquid electrical tape like I used sealing up some splices?  

[asnowman]

16 hours ago, HRemington said:

This was indeed it exactly, just as boz and gary also said.  I found the spot where the brown and yellow first go into the left side of the frame.  Sharp edge and a bare spot worn through on the brown wire.  I guess just tape it up, maybe with liquid electrical tape like I used sealing up some splices?  

Liquid electrical then tape, and i would throw a prtective sleve on it too, since you know there is an issue there already. Of course you could fix the sharp spot on the trailer too, or at least file it down a bit to prevent future issues.

[HRemington]

7 hours ago, asnowman said:

Liquid electrical then tape, and i would throw a prtective sleve on it too, since you know there is an issue there already. Of course you could fix the sharp spot on the trailer too, or at least file it down a bit to prevent future issues.

Yeah I agree.  All of the above.  But for a 23 year old trailer, not surprised.  Thanks guys.    

[electricjohn]

First thing I do with any new trailer, and not just boats, is run a separate white ground wire and eliminate the frame as a ground conductor. Growing up on saltwater and launching almost daily leaves you no choice.