That is essentially all I am doing. The 4 way connector that plugs into the trailer's pins are:

1]Ground
2]Tail Lamps (both)
3]Left Turn/Brake
4]Right Turn/Brake

I have it grounded, and the tail lamps and right turn/brake work fine. It is just left turn/brake that I have a problem with. So I tapped into my truck's factory left turn wire, and left brake wire, and connected them to the left turn/brake wire on the 4 way. Turn will work fine without the brake wire connected, but brake will not work fine without the turn wire connected. With them both connected, turn works fine until the brake is applied, then it stops working and nothing is lit.

 

Sound like one of two different things is happening,either you have two different sources colliding or more likely you are pulling more current than the circuit can handle,if thats the case go get yourself some of the LED replacement bulbs and put them in your trailer lights and see if that helps,if it does you might also want to put them in your truck. Some like this, http://www.signaldynamics.com/products/bulbs/1157.asp they draw much less current than a regular bulb.

 

I have two different sources colliding, I'm just not sure how to make the two sources oprerate on the one wire.

I have been testing with the trailer not even hooked up. My aftermarket 4 way connector has LED indicators on it so you can test without the trailer. I do like those LED trailer lights though. If I ever have problems with my trailer lights, that's definitely what I will replace them with.

 

The only thing I catink of is to add a diode inline to prevent the clash of the two forces. A diode is like a backflow preventer for electricity. You will have to reseach to get it sized right,I'm sure a google search on diode sizing chart or something like that will turn up what you need.Other than that I say replace the fusebox.

 

Thanks for your help Bluesmanjesse. I haven't been able to find a used fuse panel in a junkyard anywhere, and I'm kinda scared of buying a used one anyways, it could have it's own issues as well.

I just can't help but think that someone else out there has to have successfully tapped into their truck lights and made it work. Maybe someone else will read this that has and provide some help.