Okay... electrical gremlin.

My wife uses this truck for work. Monday night while at work, she left the lights on and killed the battery. Given the audible warning that the truck usually makes when the lights are left turned on, I couldn't understand how this could happen. Anyway, some good Samaritan gave her a jump start and she made it home. After the jump start, the only problem she noticed was that the instrument cluster was not lit.

Thinking little of it, I looked at a wiring diagram, found Fuse #17, replaced it with a new 15A and sent her on her way, assuming problem solved. On her way home that night, when she turned the lights on while driving home, the lights stayed on for a few minutes, and the fuse shorted out.

Again, she made it home.

Upon investigation, I noticed that she lost her nighttime running lights along with the instrument/radio cluster lights. But, if you hit the brakes, the lights come on. The flashers and the emergency flasher works, lighting all pertinent lights on the cab/parking light system.

I put a 20A fuse in and tried to get it to replicate the problem. I messed with the switch, checked the connectors, and made sure the fuse receptacle was tight and corrosion-free. I've traced all the wires I can get at thus far, and all wires show continuity. Next thing I'm going to have to do is start performing voltage drops on each line.

I haven't found G202 (which is a ground for Fuse #17) to check if it's tight. According to the wiring diagrams, the Vehicle Security module also contains a park lamp relay that could be a problem, but I'm not sure where the VSM is located. The only thing I see under the dash is the CJB with the fuses.

So... I sent her on her way AGAIN. She went to work, and when she left, she started the truck, turned on the lights, and while loading it up, she slammed the rear passenger side cab door. The 20A fuse popped.

She got home and I put another 15A in it and tried to verify her complaint. I turned on the lights, played with the dimmer quite violently, abused the headlight switch a little (hoping it might crap out if it was bad), and even opened and slammed every door on the cab.

Nothing. Fuse won't blow.

As of right now, I've been going outside and starting the truck every hour, turning the lights on/off, and trying to get the fuse to blow in MY presence. It won't.

Any suggestions? I'm at a loss.

 

Couple of things:

Do NOT oversize the fuse. The fuse's amperage rating was selected to protect the wiring in the load circuits so that the fuse would blow but the wiring doesn't let out it's magic smoke in the event of a short circuit.

You won't find that a proper ground (G202, for example) is causing a fuse to blow, you'll find that the problem is an improper ground. That is, there is a shortcut current path that is making a "short circuit" to ground instead of the current passing through the load.

The VSM, if equipped, is up under the left hand side of the dash. I would consider it to be a suspect only if the fuse blows while the main light switch is in the OFF position and that the Autolamp function, if present, is not also ON.

Unfortunately, an intermittent short circuit in a circuit as extensive as this one will, ultimately, drive you crazy. Unless you give up first, you'll likely find that you have a pinched or chafed wire or a defective bulb with an intermittent short.

The good news (if any) is that if it shorts completely, it then becomes much easier to find.

 

The best thing I could have hoped for was "I have an '04 and here's how I fixed it!". I knew it was a long shot... what you've said is pretty much what I had already concluded. Killing the battery must have just been coincidence. It's not safe to drive after dark thanks to this fuse problem, so I'll be spending some quality time with my Fluke.

 

change the position of the steering column and replace the fuse with a correct one. if the fuse does not blow, you have a short within the steering column . There's a few wires in an easy to reach once you pull the column neck that are the subject of a few yuotube videos related to phantom fuse blowing.

 

Correct fuse has been in there. At last report, the truck was behaving and it's gone about 50 miles today. I texted her to pay attention to the steering wheel, angle, and when turning it.

This truck was stolen in 2011. I got it back a few weeks later, found abandoned in a hotel parking lot, parked neatly where it probably just ran out of gas. Only damage was to the door lock, and the ignition was punched out. I will take a better look in there tonight.

 

F17 circuit doesn't go to the steering column...

 

My 2004 F250 6.O is doing the same thing. I am going to start trouble shooting this weekend.