check your trailer plug pigtail and the connections to your rear light harness.
somewhere between the switch and the lights you have a short to ground. my bet is in the trailer pigtail and the usually crappy connections there.

 

Good. Details are important, that is why they are required.

Aux relay box is under the hood, somewhere back near the corner between the brake master cylinder, the hood hinge, and the fender rail. Look for any small boxes and pop the covers off them. #4 has three relays in it - one large and two half size units. The two smaller ones are for your trailer brake/turn lighting circuits.

Install a new fuse, then with the ignition switch in RUN, alternately set the turn signal to left or to right and observe which position causes F6 to blow.

If it's the left turn signal that causes it, concentrate on the YELLOW wire that goes to the towing connector.

If it's the right turn signal that causes it, concentrate on the DARK GREEN wire that goes to the towing connector.

Note: Stepping on the brake pedal causes BOTH the left and right signal on the trailer to come on. The above will pinpoint which side is actually the problem.

 

Neither left or right turn signal causes it to blow, just the brake pedal itself

 

That *should* be impossible since all pressing the brake pedal does is activates the left and right trailer turn signal relays at the same time.


Pull both relays out and inspect them for damage. If none is found, put in a new fuse, and hit the brake. If the fuse doesn't blow, put in one relay at a time and retest and see which one, when installed, cause the fuse to blow.

 

Well, fellas I found the problem. I decided to start at the pigtail that's mounted to the inside of the bed for the gooseneck trailer. When I pulled it out I immediately found what the problem was. When it was installed they drilled a hole through the side of the bed liner and inner bed. The problem was when they screwed the pigtail housing in they only screwed it in to the bed liner, allowing the housing to rest on the sharp edge of the bed. After 12 years it finally wore through the housing causing it to short out. So stupid!! So thankful for everyone's help and input. Now to install a new one the RIGHT WAY

 

 

Wow...glad you found it.

 

Thank you for reporting the solution.

 

my F350 is popping the brake light fuse for no reason at all just now, nothings been altered and my truck is pretty much electrically a virgin. Back to the previous post about checking relays... I assume there is one for each side? where are the turn signal/brake relays? sorry I should add my blown fuse is #13 I believe?

 

Of course there's a reason, there is a short circuit to ground. Fuses don't just blow by themselves.

 

hard to imagine how this could happen over night with factory untouched wiring throughout the truck... any tips on where to start? btw, turn signals work fine, emergency blinkers all work fine. maybe its the switch on the pedal or 3rd brake light maybe?

 

I can imagine at least two ways (and that's from a guy whose wife says he has no imagination).

1. Critters that chew wires.

2. Non-performance of recall 05S28 (leaky switch).

3. I'll also include random bad luck, but that doesn't take an imagination.

Unfortunately, you haven't provided any information as to WHEN the fuse blows.

 

it blows as soon as I push the brake pedal down... and I keep my truck inside a huge steel building away from the elements and critters...

 

You'd be surprised where critters can get to..

Your 01 is of a prior generation electrical system from the 02 that this thread was originally about. All of the specifics regarding relays, fuses, etc, in the above posts do not apply to your truck. One of the hazards of hijacking old threads.

 

I would start with the 3rd brake light, then pull the lights out of the bed and inspect for damage. Check the bulbs and light sockets. The brake switch. And just a good thorough inspection of the wiring in general under the truck. Mice and chipmunks will find their way into places that you'd never imagine!