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Author Topic:   Trailer Lights Blow Fuse
Royboy posted 09-21-2006 07:43 PM ET (US)   Profile for Royboy   Send Email to Royboy  
I'm having an odd problem ever since I changed from the factory pig tail to a Reese Adapter. The factory wiring is corroded from too many salty Winters, so I replaced it with a Reese brand harness that plugs directly into the tail lights on my 2000 Ford Ranger. There is one plug for each side, and they can't really be installed wrong since they have pins to prevent getting thenm into the vehicle plugs backwards. Everything works fine, until I take off and then my I/P lights go out (due to a blown fuse) along with the trailer's running lights. Everything else works as advertised: turn indicators, brakes lights, hazard flashers. I'm stumpted, and I can't tow after dark until I get this fixed. I have a multimeter, but what am I looking for?


Royboy posted 09-21-2006 09:04 PM ET (US)     Profile for Royboy  Send Email to Royboy     
I have one of those little idiot testers plugged into it and it lights up properly (I think) and doesn't blow the fuse. When I plug the trailer in, the fuse blows, but I'm not sure yet if it's in conjunction with applying the brakes or a turn indicator. I'll know tomorrow when I try it out again. Tonight I took the tail lights back off the Ranger and checked for bare wires, I didn't find any, but I added some convolute sleeving just to be sure I don't have any stray contacts with the body.


fno posted 09-21-2006 10:08 PM ET (US)     Profile for fno  Send Email to fno     
You are looking for a short to ground in your trailer wiring most likely. Take your voltmeter, put it on ohms and check for continuity from your leads to the trailer chassis. Only one should read zero ohms, the wihte one usually. If any of the others do read zero ohms then you have a short that is blowing you fuses.
jimh posted 09-21-2006 10:43 PM ET (US)     Profile for jimh  Send Email to jimh     
You need an accurate ohmmeter. A cold bulb filament will measure almost as low as a direct short.
Chuck Tribolet posted 09-22-2006 12:46 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
So take the bulbs out. But first do an eyeball inspection
of the trailer wiring.


PeteB88 posted 09-22-2006 09:54 AM ET (US)     Profile for PeteB88  Send Email to PeteB88     
Rodents stripped yards of wiring in my Karavan trailer - took awhile to figure that out but it was amazing. It kept blowing diode in trailer light converter necessary for Camry. I knew there was a short but could not determine extent until I pulled out the old wiring - at least 40% was stripped bare. When in doubt you might want to rewire - not a big deal.
Buckda posted 09-22-2006 09:56 AM ET (US)     Profile for Buckda  Send Email to Buckda     
Look over your wiring carefully. I had a similar problem earlier this year and solved it by rewiring the trailer. It's a fast, cheap and easy task that only really requires Plastic Zip Ties as a temporary measure to hold the wiring on. When I was able to inspect the wiring, I noticed a short where the wire had rubbed against the threaded bolts that hold my guide-ons in place.

Wiring kits are only like 25 bucks, and you should go to NAPA and buy about 5 extra fuses now so you don't have to keep going back.

Also -

If your hazards work you can still tow if night falls on your trip - I had to do that on the trip to Leland over the 4th of july (which is when my problem manifested itself).


Royboy posted 09-22-2006 10:28 AM ET (US)     Profile for Royboy  Send Email to Royboy     
Thanks everybody. I have re-wired trailers before and it's not a big deal. I'll spend a little quality time with my multimeter first, however. Good suggestion on pulling the bulbs, Chuck.

Dave, I've had to resort to the hazard flashers twice now to get me back from Lake Erie. I also found good use for my handheld GPS as a speedometer, since my I/P lights go out when the fuse blows! I really don't want to do that all the way up North though.


jimh posted 09-22-2006 11:17 AM ET (US)     Profile for jimh  Send Email to jimh     
It is rather difficult to remove the bulbs from sealed enclosures. It is also a lot of work.
Royboy posted 09-22-2006 06:27 PM ET (US)     Profile for Royboy  Send Email to Royboy     
My lights are not sealed, so no problem there. I took the bulbs out of the two tail lights and the meter reads open on both the green and yellow wires. The brown wires read zero, as does the white one. With the bulbs in, all wires read zero. Am I getting anywhere?

What completes the brown wire circuit?

One of the clearance lights has a bad connection, so I'm going to replace that and see what happens.


Chuck Tribolet posted 09-22-2006 08:30 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Green is right turn and brake.
Yellow is left turn and brake.
Brown is tail, running, and over-80 lights.
White is ground.

(over-80 lights are the three lights in a row mounted as
hight up on the vehicle as possible (on a boat trailer this
means UNDER the boat ;-) that indicate that the vehicle is
over 80" wide).

If you have running lights, take those out too.
If you have over-80 lights, disconnect or take those out.
Now if you still have zero Ohms on the brown to white
connection, you have a wiring short somewhere. At that
point, I'd just rewire, with all Ancor marine grade wiring.


Royboy posted 09-22-2006 08:43 PM ET (US)     Profile for Royboy  Send Email to Royboy     
I don't have over-80 lights, but I do have clearance lights on the leading and trailer edges of the finders. I'll shoot this thing again in the morning.


Jakwolf posted 09-22-2006 10:57 PM ET (US)     Profile for Jakwolf  Send Email to Jakwolf     
Roy, I had the same occurance at the ramp after aday of fishing Half Moon Bay. I plugged the trailer lights in a pop! Long story short, direct short from the over 80" light bar at rear of trailer. So as suggested, look for the short. Mine was not visible, I cut the brown wire at the rear before I figured it out.
Royboy posted 09-24-2006 12:30 PM ET (US)     Profile for Royboy  Send Email to Royboy     
Well what do you know...I do have "Over-80" lights. I replaced all four clearance lights, mainly because one was suspect. I checked all of the visible wiring and it all looks good. There are nice rubber glommets through which the wiring passes to get inside of the triler tubing, where of course, I cannot see. There is enough slop in the wiring where I can pull some through to check for breaks, but it really doesn't look like the wiring itself is the culprit. I can't rule it out, but for now it seems fine.

Everything seems to be working, but I'm going to give it the acid test this afternoon. We'll see if everthing still works after I dunk it in the water.


PeteB88 posted 09-24-2006 02:25 PM ET (US)     Profile for PeteB88  Send Email to PeteB88     
You might use liquid electrical tape on the connections - esp those that are likely to get dunked when you launch. Messy but works great - a couple of applications. Starbrite is one manufacturer.
tashout posted 09-26-2006 01:20 PM ET (US)     Profile for tashout  Send Email to tashout     
just happened to me. check your side marker lights . probably a wire that is shorting out on the chassi of the trailer. find where the plastic coating has worn cover with electrical tape and your good to go.
Royboy posted 09-29-2006 12:57 PM ET (US)     Profile for Royboy  Send Email to Royboy     
So far tashout wins the prize. I drove all the way to work with the running lights on with no problems. After work, we'll dunk her in Lake St. Clair and see if it wasa the side markers after all.


Royboy posted 09-29-2006 09:44 PM ET (US)     Profile for Royboy  Send Email to Royboy     
It's official: Tashout Wins! I apparently had a bad marker light. I gave her the acid test this evening and the lights worked perfectly all the way home form the lake. Thanks everyone for your input and help.


17 bodega posted 10-07-2006 11:44 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
I have been having the same problem on my jeep and trailer lights. Connecting my trailer light plug ( a 4 flat adapter into a Chrysler 7 prong outlet that tests ok at the plug adapter) blows my left tail light fuse in the jeep dash. I have purchased a "Wesbar" 4 flat wiring kit to re-do the trailer with. This appears to be the OEM trailer harness minus all the marker light crimps. I have also purchased new Worst Marine LED trailer tail/turn combo lights. My trailer also has marker and rear running lights that run off the brown tail light wire.

Does anyone have a wiring diagram or schematic that details the wiring procedure of a trailer using the OEM type of 4 flat wiring harness? I also notice that in the rear of my trailer, there are brown/yellow and brown/green striped wires that seem to be crimped to the brown wires on each side.

One thought that I had is to ditch all the marker lights and just get the dang tailights and turn signals to work, and add the marker lights later.

Any tips or advice would be appreciated.


17 bodega posted 10-07-2006 11:46 PM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Do I legally need the marker lights and the "Over 80" light bar in the rear?

Maybe I'll take Chucks advice above and pony up for the marine wire. Does anyone sell the 4 flat harness with marine wire?


Chuck Tribolet posted 10-07-2006 11:52 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
State laws vary. In California, if your trailer is over 80"
wide, you must have the over-80 lights, and you generally
also have to have the the side marker lights.

How big is your boat? Anything Montauk size and up will need


17 bodega posted 10-08-2006 03:05 AM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
It's the old blue 16 footer you saw at the 2004 Snug harbor event. The trailer is an EZ loader with all the extra side markers and 80 wide lights.

I will try to best imitate the existing setup with new marine grade wire and shrink tube connectors and the liquid electrical tape

It sounds like I should double check all the ground wires too.

17 bodega posted 10-08-2006 03:06 AM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Oh yeah... one other thing that is strange is that the trailer lights would light up for about 15 or 20 seconds before blowing the fuse...

Chuck Tribolet posted 10-08-2006 09:42 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
The slow blow just shows that the trailer lights have an
imperfect short. It's only barely enough to blow the fuse,
so it takes time for the fuse to heat up and blow. It's also
possible (not likely) that you used a Slo-Blo fuse which is
designed to blow extra slowly.

The Ancor catalog shows 16 ga. four conductor flat cable with
trailer color code, though last I looked, they didn't show
the connectors.


17 bodega posted 11-05-2006 10:58 AM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     
Regarding trailer wiring, it looks like EZ LOADER wired my trailer with a brown/yellow on the right side and a brown/green on the left. The white ground wire is only run to the chassis near the tounge and grounded to the chassis in several other locations. Then a common brown is run all the way around the trailer for the marker lights, tailights, and 80 wides. It looks like the common brown is tied in at the right tailight using wire crimps. Then it travels to both tailights, the 80 wide and marker lights.

Also, in very short order, a brand new west marine LED trailer light wire corroded and turned black. I am inclined to discard this light and buy a new one when installing the new wire. I will use a dremel and wire wheel to remove the corrosion from the chassis. Can anyone reccomend a galvanizing spray for the bolts to avoid future rust?

Chuck Tribolet posted 11-05-2006 11:32 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
Was that West trailer light wire plain copper (bad) or tinned

Splitting the brown at the taillight is a bad idea. It
should be split someplace it will stay dry. When I get
round to rewring my trailer, I'm going to tuck that
stuff up inside the winch stand.

Use SS bolts and SS star washers under them. The SS star
washers are hard to find, but I've got a bunch of them (had
to buy boxes of 50 from McMaster to get two). Let me know
what size you need and I'll mail them to you.


17 bodega posted 11-06-2006 12:43 AM ET (US)     Profile for 17 bodega  Send Email to 17 bodega     

You are right on my line of thinking. First of all, the West Marine tailight wire is (bad) copper and I was able to exchange it out today for a new one.(still bad but new) Hopefully soon a manufacturer will step up to the plate and build a truly sealed saltwater LED trailer light kit with the proper wires and LED rating.

I will do as you suggest and tie in the wire at the dry end of the trailer. I was wondering why a seemingly competent operation such as EZ LOADER would wire a trailer in the manner they have. The materials upgrade would seem nominal and well worth the extra cost.

Also, the galvanized nuts and bolts on the tail end of the trailer are barely usable and 3/4 size. I'm not sure the thread size but I'll look into that. The 80 wide light bar is toast also, so I will attempt to use the steel mount but replace all the lights with the LED marker lights. There is a great hardware store in Petaluma that has a vast inventory of stainless steel fasteners by "Hillman" which is the brand I think West Marine uses.
I did score some great deals on primary ANCOR wire at the Worst Marine bargain store today. I got a 500 foot spool of 16 gauge ancor wire for 30 bucks and another 500 foot spool of 18 gauge for $20. I would have bought more but that's all they had.

Thanks for all the great insight on saltwater wiring.


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