Electronic short

[Bigfishhunter]

When I hook up my trailer to my truck I have been blowing fuses automatically. What goes is the fuse that runs my running taillights for both the truck and the trailer. Brake and signals still work, but if I wanted to run in the dark, I can not do now.

I am wondering if you think it would simply be an issue of a short in the trailer (where it may be pinched or rubbed) or if you think it is an issue with the truck harness itself. A little history on my truck. I bought it in the U.S. last year, and in Canada I had to get a module put in so that it would have daytime running lights to meet the safety. Well I got the dealership to hook up a trailer harness at the same time. :huh:

[northernbite]

I would say you have a short from the way it sounds. It happened to me last summer, went home and re-wired trailer.

Paul

[Bigfishhunter]

yeah that was what I thought would be the easiest, just rewire it up, and see what happens after that.

[Stringbean]

As long as you are going to rewire the trailer, I would wrap the leads with spiral wrap. I think I got mine at Home Depot. Just wrap up the wire as you feed it into the hole in the frame to go back to the tail lights. That should take care of the abrasion from the inside of the trailer frame.

[ffishman]

Why not try plugging it into a friends truck and see what happens

[REW]

Before doing anything - go and pick up a wiring checker:

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_200307153_200307153

By using this tool, with good fuses in the truck you can check your truck wiring. You should be able to turn on your tail lights and see one led light.
Then, one turn signal and see one led light.
Then , the other turn signal and see one led light.
Finally, hit the brakes and you should see both of the leds that lit up when you hith the turn signals.

Then, take a battery and set it next to the trailer - You can also use a pair of jumper cables from your truck battery to the trailer hitch.
Now, take a short jumper wire from each battery terminal or jumper cable and touch the correct terminals on the trailer connector plug.
The one connector that is different will be the ground connector and should be connected to the negative battery terminal or jumper cable.
Then - going one connection at a time, you should ba able to light up the tail and clearance lights.
Then one turn or brake light.
Then the other turn or brake light.

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If you have a short in your trailer wiring, you will likely get smoke and no lights when you connect one of the connector pins to your battery. This will be the circuit that is causing your problem on your trailer.

It could be taile and clearance lights. Or it could be the right or left turn signal.

Once you have figured out whether it is a truck or a trailer issue, you can fix the problems.

If you don't get correct lights being lit on the test plug from your truck, you need to fix your truck. I would then assume that you would get correct operation when using jumper wires to power your trailer lights.

However, if you get correct operation on your test light on the truck, I would assume that your truck is all right and that you will likely get smoke due to a short when you connect one of the trailer light connectors.

--
Of course you could have an intermittent condtion that only happens when a trailer goes over bumps causing a wire to rub and short due to trailer movement.

If you don't find issues with either truck or trailer - you can likely assume that you have an intermittent condition on your trailer and I would suggest that you pull in a new wiring harness on your trailer and rewire all of the lights.
If your lights are old, it might be a good time to upgrade to LED trailer lights.

Take care
REW

[Shep]

Are all the bulbs in the side markers? I've seen some where the socket will short if the bulb is not in it.

Most likely, you have a wire shorted somewhere inside the frame of the trailer. Not likely that it is in the tow vehicle. Brown wire is for the tailights and sidemarker lights. If you have a brake release solenoid, it could also be shorted, and that could take out the fuse as you shift into reverse, depending on the tow vehicle.

DO NOT test with a battery unless you have the connections fused! Very bad idea. You could cause a fire, or burn yourself when the wire "smokes". An multimeter is the best, and safest, way to test for shorts and operation.

[Smitty]

Good advice from Shep. Assuming you're blowing the fuse immediately when you hook up the trailer and turn the lights on, here's what I would do:

1. If you don't already have one buy an inexpensive multi-meter (trust me, it will prove invaluable many times). You can get low end ones for $30 or less at Menards, Sears, etc.

2. With the multi-meter set on DC Voltage check the voltage output from the pickup. With the lights on you should have 12v on the brown wire, and with turn signals on you should see 12V on the green and yellow wires respectively.

3. Make sure the wires on the pickup end match the wires on the trailer plug (colors match up, just to make sure they didn't cross a couple wires on the installation).

4. If everything is ok at this point the issue likely isn't with the truck. At the trailer end it gets a bit trickier.

5. With the meter set to ohms check to see if the brown wire on the trailer plug is shorted to ground. Depending on the accuracy of the meter you may have to pull/unplug the bulbs/lights as you'll be reading resistance through them to ground (so it won't be an "open" connection). If you're still reading a short to ground after all lights are unplugged or pulled then you have a nick somewhere in the brown wire in the trailer, likely spots are anywhere the wires come out of the frame to run to the light fixture. If it's something easy and you can see it, a bit of electrical tape (or better yet liquid tape) and you're all set. If not you have to make a decision as to whether to keep searching or just install a new wiring harness.

If it's broken solid rather than intermittent it's generally pretty easy to find. On my ShoreLandr last year I had a wire pinched that goes to the light(s) that are mounted on the rear crossmember. Since you have to unplug everything in either case, might as well see if it's something simple before you go to the effort of rewiring the entire trailer. If you do rewire, use pullstrings on all wires when you remove the old harness to assist in pulling in the new wiring.