Here's one for you electrical systems experts. I bought a brand new snowmobile trailer the other day. I hooked it up the 4-pin harness - strange things be a happening!

With the headlights ON the trailer only lights up one rear taillight

When I apply the brakes both brake lights illuminate and so do the marker lights

When signalling a left turn the right turn signal and the left marker lights flash

No kidding

First the obvious - connection tight and general wiring of the trailer looked okay the correct color was going to the correct place on visual inspection. The 2-pin bulb connectors looked okay as well. All the trailer lights work - they just don't work when they are supposed to sort of. So the basic set up is okay and trailer is made by a reputable brand (Floe). I wasn't able to find where the trailer grounds to trailer frame.

The first quesion - does it look like a trailer problem or a truck wiring problem. Second does anyone have any thought on where to go with this. I am taking it in to Ford next week to rule out a truck problem before pursuing the trailer folks. I'd like to try to fix it myself - I'm one of those

Thanks to anyone who can offer assistance and suggestions

 

The first thing you have to do is eliminate what the problem IS NOT. My first step is usually to isolate the problem to either the truck or the trailer. To do that, there are a number of inexpensive testers out there (I built my own) that plug into the end of the trailer plug on the truck. Assuming (and I would with an '04) that your truck is not the problem, you'll need to trace the problem down in the trailer.

Now trailers can get a whole lot more exciting - even a well built one. The number one problem I find with trailers is bad grounds - to the tow vehicle. I'd check for that first. (It's the white wire.) The second biggest problem I run into is corroded sockets and / or bulbs - which can also lead to a bad ground. I use a special corrosion resistant grease (NPK Light Bulb Grease) to prevent corrosion on new stuff. On older stuff that has already corroded, you can try sanding off the rust, but you're going to end up replacing the stuff.

Try that and get back to us.

 

Try pluging your trailer in someone elses truck to see if you get the same results.

Same result = Bad trailer wiring

If Trailer OK on someone elses setup, Go see your Friendly Ford dealer.

I suspect either the trailer connector or the truck connector has 2 wires that were crossed (Not Shorted) I mean the Left Brake light/left turn wire was put where the Park light goes and vise versa.

I'll bet it's the trailer if your truck came with the towing package factory installed. But then again, if your truck was built on a Monday morning or a Friday afternoon...

Dpostman

 

This is a dumb question for me to ask, but are the bulbs OK? I mean are they single filiment or dual filiment bulbs. It could be that one of the filiments in a single bulb is burnt out, but not the other.

Tony