I've noticed that with all my trailers that when im running my lights(driving at night) the trailer lights dont illuminate, The brake, and turn signal light all work. So since its happening between several trailers im guessing i have a bad fuse. What fuse would this be? This is on my 05 250 btw. When towing these same trailers with my 350 the lights work fine.

 

The pin could be bent or disconnected on the receiver. Check the wiring going to the connector on that vehicle. I believe it is the green wire.

 

Check fuse 38, a 20 Amp, under the dash.

 

the connector looks good from what i could see, its dark out. the fuse also checked out

 

Got a voltmeter? Bust it out and test the ground and the green... which is technically 5:00 if the post is at 12:00, which is also where the ground is.

 

Dont have a voltmeter, i just dont understand what else would make it stop working

 

Broken/bad connection, bad wire, bad contact, etc. A voltmeter will confirm that. Sears has em dirt cheap. AutoZone may even test it for you for free...

 

I would start by using a small pick that has a 90 degree bend in it to re bend out the pins on your trailer light socket on the truck. These pins wear down and bend closed so they don't interact with the trailer plug as well as they used to.
This happens more and more the more the trailer light socket is used.

After this I would start with a volt meter, seeing as you have already checked the fuse.