We have a 2002 F150 XLT two wheel drive super cab V6. Wednesday my wife was coming home and she said the turn signals went out. I found fuse #13 blown, so replaced it tested the turn signals and all was good. Thursday morning we both left at the same time, I happened to be following her, we get to the end of the road and she comes to a stop and uses the turn signal.. the turn signal quit working. Thursday night I attempt to test a few things, unplug the fire stick (aftermarket turn signal), the brake lights were not lit. I replaced the fuse again, tested and all was fine. Figured the fire stick was to blame. Started truck turned head lights on, tried turn signals, hazards, brakes, everything at once all was good.. Wife called shortly after she was on the road (a bit longer this time) fuse popped again. Tonight I have removed the trailer plug, tried to locate some issues with the wiring harness, looked at wires in the steering column, tried everything without the truck running everything was fine, working. Decided to start truck and test drive.. start it, turn on headlights, turn signal activated blew fuse.... now I am beyond frustrated. One attempt before removing the trailer plug, was replace fuse, hit brakes and it blew, replaced tried hazards it blew. I have gone through 8 fuses which is not expensive, but getting there.. and a pain.. not sure how to use a circuit breaker to avoid the fuses for testing purposes.

I am looking for any advice. I have a feeling it has to be a short? How should I begin? As mentioned i followed the wire harness from the back with the trailer plug to the front engine fuse box. It honestly looked good, no issues, no splices, looked original. It makes me think it has to be the turn signal/hazard wiring somewhere... Thanks in advance, I hope to defeat this before I have to give up.

 

could have a shorted light bulb?

 

Yes, it is. It's also intermittent which will complicate matters.

It cannot be the trailer wiring harness as everything there is isolated by either dedicated fuses or relays.

Does this truck have a cap or topper installed? If so, check it's wiring as it's often done as a hack job.

Since the issue has appeared when the brakes have been applied, the hazards or a turn signal used, the issue has to be in the circuits to the rear of the truck only.

Eliminate the high mount stop lamp since it isn't energized in hazards or turn signal mode.

A good prospect. Pick up a pair of replacement bulbs (and more fuses). Pull out the rear tail light assemblies and inspect the visible wiring. Inspect for water trapped in there. Replace the bulbs on both sides if nothing shows up in the inspections and then re-test.

What, specifically, is a "firestick" and how is it connected.

 

The "fire stick" is an LED tailgate light. It lights up when turn signals are activated, and brakes. It gets it's power from the trailer 4 pin plug. That is not it, as I have cut off the 4 pin plug from the truck. The plug did have some corrosion (green) in the brake light wire pin. However that is no longer attached to the wires. I will set out to search the lights, and get more fuses. Honestly the wires from front to back look good. The truck does have a topper on it, but it has been on there for a long time. However it is not to say the wiring finally gave out. I did notice that the cab third brake light is not functioning, although I am not sure if there is a bulb in it since the topper covers it. And as I am typing this, not sure if there is a light in the topper and if it works. I am sure there is, will need to check that.

Thanks for the help and advice. Will attempt the bulbs and lights first, then wire tracing. Just not sure how to trace the wires?

 

Does the topper have it's own corner brake lights and signals or is it a simple shell? Its wiring is only a suspect if it has it's own signal lights or if it uses the individual signals from both sides to turn on a single high mount stop lamp. If it's a simple shell with no brake or turn signals, then its wiring is probably not a suspect.

Why have I now focused on the topper since you said you had one? Too many of them have had the vehicle wiring hacked into and wires often rub against the sharp edges of holes or are run between two surfaces, one of which is metal, that eventually wear through the insulation of the wiring and cause a short circuit to ground.

 

The topper does not have any lights connected, so that is not the issue. Great thought, but checked that over this morning.

Here is what I have done today. Replaced every bulb for turn signals/brake lights. Replaced the third upper brake light (that was burnt out). Cleaned all the bulb connectors. Cleaned the battery terminals. Started it and drove it twice with no blowing fuse. Not sure why, still not pleased as I did not find out why it was blowing.

Will know more when it is driven a bit more. Have a feeling it is the left turn signal, as it appears to have blown more with the left turn signal being used.

 

We just recently went through a diagnostic tree on the forums here lately with a guy with a worn harness in the door hinge area that was blowing fuses with left turn signal.



You don't need a circuit breaker to diagnose this. Here's a helpful tip.


http://www.crookedriverwriter.com/in...-shorts-faster

Follow the setup procedure above, and start eliminating sections.

Go through and start unplugging branches of the circuit and quickly eliminate large sections of the wiring, once you have it narrowed down to a small section of the entire circuit, you can do a thorough visual inspection and repair it. In some cases it might be easier/faster to just overlay the effected wire.


That trick works really well, and its quite simple. Basically your fuse is popping because there isnt enough resistance (short to ground) and draws too many amps, thus popping the fuse. Adding the sealed beam adds resistance to the circuit between the short and the power source, aiding in diagnosis and pinpoint.

 

Update... Yesterday after putting it back together and running it a few times, putting it through all the tests (lights on, brakes, turn signals, etc.).. the fuse did not blow. Went to work (a 40 mile trip one way) in the morning no problem. Coming home from work all good till 5 miles form home. Lights on, left turn signal and fuse blows. Got home, replaced fuse and again no issues. Left truck run for 5 minutes with brake applied, lights on, and left turn signal on... issue.. Wife is taking it back to work tomorrow, with instructions on how to replace the fuse... and not to replace more than 2 if it blows immediately. And there was no rain today, only cool damp morning about 50 -52 when leaving for work.

Very stumped... going to try the sealed beam method, just need to get a sealed beam worthy of using...

 

Might also be worth checking the harness through the column, especially around where it articulates for the "tilt" function