Trailer light help please

[steve(IL)]

I've got brake lights and turn signals, but no running lights. I'm an admitted amateur with the meter, but I don't appear to have power anywhere in the running light circuit. Any advice will be greatly appreciated!!

[Phil T.]

Since my boat is 18 years old, I may be qualified to try an answer to this.
First, were your vehicle's headlights or parklights on when you tested the trailer running lights? I don't mean to be insulting, but we'll start with the simplest possible problem. Also check the tail light bulbs to be sure they have two filaments each. One for brake/turn, the second for tail lights. Clean the sockets and grease them.
Second, what is the condition of the wiring leading to the vehicle's plug? Do you have voltage there? Was one of those 3-way connectors used to connect to the vehicle wiring? If the included waterproof grease wasn't used when that was installed, the internal connections commonly corrode.
Next the condition of the trailer's plug. Is there voltage at all the wires leaving that? You can nick the wires to get the voltmeter probes on the wires, just cover the kicks with electrical tape or that liquid tape stuff after you've tested them. Don't forget the ground wire.
If there is power this far, check the first connection where the trailer plug is connected to the actual trailer wiring. If he connections were made with those ****ed 3M clips, get rid of them and solder-connect the wire splices. Cover with liquid tape and armor-plate the connection with heavy electrical tape.
Any other faults will be in the wiring that runs inside the trailer tubing, or at the light units themselves. Check the wiring where it attaches to the lights.
My trailer has the usual two taillight assemblies, the three little lights under the rear of the trailer, side marker lights on the tongue, and clearance lights on the fenders. Every one of those bulb sockets are likely to be corroded. Most of the time, I'm happy to keep the two big rear lights working. If I can get 80% of the others lit at any one time, it's a good day. Dunking 12v electrical devices in the water when launching and retrieving a boat is by it's nature, dumb. Be sure to disconnect the connector plugs before dinking the lights to avoid blown bulbs. Yah, those light assemblies are waterproof, but manufacturers have been known to lie about other things, too.
Good luck, sometimes an obvious problem takes a few trials to find. Maybe these irritants are needed to build character.

[David/MN]

Are you towing with a Ford? If so the is a second fuse in the power distrubution panel under the hood that should be checked.

dw

[steve(IL)]

Thanks David & Phil. Yes, it is a Ford so I'll check the fuse. I've replaced bulbs, checked connections, etc. I've encountered trailer light troubles before and had reasonable success sorting things out. This problem has been particularly frustrating. I hope it ends up being the fuse mentioned.

[David/MN]

Let us know what you find.

dw

[kappy]

I posted the same question a couple of weeks ago. And these guys helped me out quickly. I too have an F-150 and it was the fuse in the box that Dave mentioned.It's on the driver's side under the hood.A mini 20 amp was the problem.

[d_rigger]

MAKE SURE YOU HAVE A GOOD GROUND, MY PROBLEM 75% OF THE TIME.

[stein]

I have a 2000 Chevy and everything works except for my left hand turn signal and brake light. I pull several different trailers between work and pleasure and it is the same with all of them. Someone said there might be an inline fuse? Where would it be located if the harness was factory installed? Thanks in advance.

[Starfish]

More likely than an inline fuse would be a problem with the converter box that changes your separate tail and turn lights into a single signal for the trailer. Often one of the diodes in the converter box will fail and you need to replace the unit. Sometimes they do use two separate diode sets rather than a single converter box. Just follow your trailer plug wires (on the truck) back until you find the box; a replacement is available at most auto parts stores (typically $5-$30 depending on the type of vehicle).

[steve(IL)]

Dave - you were right! It was the fuse up front. Now I have a different problem - I'm blowing fuses which I take to mean that I have a short somewhere. Any advice on how to isolate a short?

[David/MN]

Same problem I had.... Look at points where the wiring comes out of the trailer frame and feeds the lights, I was missing a grommet where the wires come out for one of the side marker lights, the opening was ruff and ate away the insulation shorting the hot on the frame.....A little black tape and many more miles have passed....

Good Luck, keep us up to date...

dw

[STCROIX BOY]

My new Ranger did the same thing. I found no short in the trailer, so I put in a bigger fuse in the box under the hood. Works good. If it blows up the fuse box this summer, I'll let you know. Personally I hope it burns to the ground. Ford Junk!

[vetspet(ind)]

some of the electronic circuits will blow if you have your vehicle running when you plug in the trailer..happens all the time with my ram van...basically if i unplug when i put in and then when i get back and load up...i should turn off the vehicle and plug in...then start van again...chrysler dealer told me this one and it works....the other thing that did this before was my ground wire...steve