Fuse for running lights keeps blowing

I did a little bit. We found some wires under the rig below the driver's door that are totally hanging free. The problem is that there are three of them and no obvious place they should be attached or if all three go together.

I also found a slight rubbing cut on the wiring bundle where it passes from under the chassis out to the mounted tow assembly (where you plug in the cable for the toad). The cut is just through the plastic sheath and exposed the edge of one wire but didn't cut it so John wrapped that in electrical tape and I wrapped the giant threaded chassis bolt with duct tape so it didn't chew it again.

I haven't convinced John to let me pull apart anything in the steering column or engine compartment... Yet.

Your findings has me thinking I should inspect my wiring harness, especially in those same areas.

Today was troubleshooting day. We went through all the steps that we had done before so I could journal it and at the end of all of our testing... the lights work. We changed nothing, we cleaned nothing, we fixed nothing. I personally suspect there may be corrosion on the back of the fuse box but we are not fix-it people so we will not be pulling that. Hopefully our light situation will hold until we take the the rig to the factory this spring/summer. I intend to ask them to pull that fuse box and inspect the wiring on the back.

Possibly related question - where does the water drain to when you have condensation on the front window of the truck?

I had this issue with a Volkswagen Rabbit back when I was in the Army. There was a recall for the antenna seal. Water got past the seal, ran down the wire and got into the fuse box. I lost all my electricals one by one rolling down the highway in a storm. First the radio, then the headlights, then the windshield wipers. They fixed it four times with the final time resulting in a replacement of the fuse box itself due to the corrosion from previous water incursion.

Thank you all for your suggestions. I'll definitely be watching those lights. If we blink out again before we get to the factory, we'll be back to troubleshooting mode.

I did a little bit. We found some wires under the rig below the driver's door that are totally hanging free. The problem is that there are three of them and no obvious place they should be attached or if all three go together.

I also found a slight rubbing cut on the wiring bundle where it passes from under the chassis out to the mounted tow assembly (where you plug in the cable for the toad). The cut is just through the plastic sheath and exposed the edge of one wire but didn't cut it so John wrapped that in electrical tape and I wrapped the giant threaded chassis bolt with duct tape so it didn't chew it again.

I haven't convinced John to let me pull apart anything in the steering column or engine compartment... Yet.

Those wires by the door are likely for the step light in the doorway.  At least that's what's on my 2015 model.

Step light sounds logical. We seldom drive at night so we wouldn't notice it is out. Since I don't know if all three wires bundle together I'll add it to the PC Factory repair list. Thanks for the diagnosis

Those wires by the door are likely for the step light in the doorway.  At least that's what's on my 2015 model.

DING DING!       We have a winner. The three wires were indeed the ones that supplied the step light with ground and power. A piece of road debris ripped the wires apart. One of the wires stayed in the light housing, making three visible. Supply wires are undamaged and tested OK.  Socket is destroyed. Zip-tied the supply wires safely out of harm until the permanent repair is done.

The running/parking light fuse issue is hopefully solved. The tag (license plate) light was observed to be not working. Took the light out, then separated the bulb holder from the lens. When removing the bulb from the holder, I observed something fall out of the socket.  The insulating piece that keeps the 'hot' center wire separate from the grounded areas of the socket had broken into pieces. This allowed the center tab to contact the spring and other grounded areas. I strongly suspect that was the source of the short in the system. The bulb tested good. The 'hot' wire was wrapped with insulating tape, and the light assembly re-installed with no bulb until a permanent repair is done. With a toad behind, and no night driving, the lack of a tag light should not be an issue.

Thank you Volkeman for being awesome and bailing us out (twice). It's amazing what someone with the right knowledge, skills, and sharp, problem-solving mind can do. John and I were, once again, clueless and looked at all the different parts, analyzed what we knew, couldn't put the pieces together and came up with the diagnosis... It's broke, we'll have to live with it.

Volkeman looked at the different pieces, it all fell into place in his mind, he tested a few wires and figured it all out in less time than it takes for us to dig out our manuals.

We bow down to the amazing fix-it guy mind! You rock!

You da man Volkemon!

So what has been concluded?
Is "the following" the recommended trouble-shooting procedure for 2 Frazzled and others with the same problem?

Check every light fixture that should be lit in that lighting circuit.  Check to make sure the internal connections (and wiring to) each fixture are in good order.  One fixture might have failed or otherwise come apart internally, causing an intermittent power-to-ground short.

Start with the lowest, most vulnerable light fixtures susceptible to damage or corrosion when the rig is driven, for example the running board lights and wiring to them.

Once every light fixture in that circuit has been inspected with suspected fixtures repaired or replaced, if the failure persists, then inspect the connection-side of the fuse panel.

So what has been concluded?

In any type of troubleshooting, your most valuable tool is logic.  Your second most valuable tool is observation coupled with a general (if not specific) understanding of the system that you're trying to analyze.  In this instance Volkeman used both.

For example, in this type electrical/wiring problem, logic should tell you that the most reliable part of the system should be the Ford engineered and factory installed wiring--you wouldn't immediately start tearing into the factory wiring looms to search for this problem.  Sure, they can fail, but the fault is much more likely to be where something was added, modified, damaged, or at an interface point.  Secondly, you look for indicators.  With step light, the wires hanging free are an obvious target; they probably didn't just "fall out of the loom".  Don pointed to a likely culprit given the location.  Volkeman confirmed the situation with an inspection--and rendered things safe by securing the wires until the light fixture can be replaced.

Another "indicator" led him to the probable cause for blowing fuses.  If the tag light had not been out, Volk very likely would not have had reason to pull and examine that light--and locate the faulty socket.  Again, the problem could have just been a bad bulb--with no payoff on the fuse issue.  But the fact that he followed up on an "indicator" (one light being out when others were working), paid off in spades this time when he discovered not only the reason for the dead tag light but most likely the reason for an intermittent and elusive fuse-blowing problem.

Hats off to Volkeman for demonstrating some key troubleshooting techniques!

Mike H stated it so well. Thanks.