Fuse for running lights keeps blowing

We're hoping someone has a clue on this. We normally don't travel at night so we don't know how long we've had this problem. However, earlier this week we did have to travel at night and a trucker went by honking at us and flashing his lights. When we got off the road we checked our lights and realized we have no running lights on the RV or the toad. John checked the fuse and found the 15 amp fuse for the running lights was blown. We purchased matching fuses and when John put a new one in, it immediately blew. He said there is no sign of corrosion in the fuse box so we don't think it is water intrusion.

Any thoughts?

Actually the manual says "park lamps, license plate lamps" in case this makes a difference. Bottom line, we are running dark in the back and will only drive daylight until resolved.

Unplug the car and try again. This will at least tell you whether it’s a coach issue or a toad issue

The car has been unplugged for a few days while we've been in camp. The second fuse blew as soon as John plugged it in.

Hi Holly,

This is worth a try.

Look in your Ford chassis owners manual under fuses and relays.  I can't say for sure, but there may be a tail-light supporting relay located inside the fuse box under the hood.  If there is, try this "only as an experiment" with the engine turned off.

Identify another "identical" relay used in a different non-essential assignment, HVAC for example.  Remove it and install it in the tail light position and see if the fuse burns again.  If the fuse does not burn up and the lights work, then you have a bad supporting relay.  If the fuse burns up again, then you ruled-out the relay as the culprit.

Then revert everything back to "normal" all relays in their original positions and check to make sure your HVAC is working.

If you need a new relay, you can buy one from any auto parts store.

Usually when a relay goes bad, the circuit gets broken just like a fuse.  But once in a great while, certain types of relays will short in such a way that it creates the fuse-burning condition you are experiencing.

Please explain exactly which “running lights” are we asking about.  Do brake lights work? Turn signals? Happened once to me, water got in reflector housing and shorted out lights.  Take a flashlight and hold up to lens and see if any water intrusion.  A seal was loose and I guess it was condensation build up.

And if the above does not yield results, I would start looking at the phoenix cruiser installed trailer plug and wiring. Versus the OEM Ford wiring

I like Tarnold's idea of inspecting for water inside one of the lights.

Will makes a good point too.  I understand the extended trailer wiring on the motorhome is Ford-supplied, a connector on one end plugs into the chassis harness.  That should be extremely reliable.  The other end has pig-tails (wire ends) to connect at the trailer receptacle.  The Achilles Heel would be right at the trailer receptacle.  On our 2007 PC, that receptacle is wire-tied to the square bar of the hitch.  (see picture)  To inspect, remove the 4 screws at the connector, then slide the housing to the left to expose the connections.  Maybe the tail-light hot wire came loose and is touching a ground wire.

Our outside inspections are on hold for a day or so. It's 27° at the far Eastern Florida/Georgia line.

Brake lights and turn signals work. Headlights work.

I call the problem ones running lights but the manual calls them parking lamps. It's the lights you see as you tail a car or rig at night that has its headlights on. If we aren't braking or using turn signals, we are totally dark at the back. Rig and toad.

We should warm up later today or tomorrow and I'll check all the suggested items then.

Good luck, there are a lot of Phoenix cruiser installed lights connected to that circuit. Good thing we didn’t head to Florida to stay warm.

Holly,

There is no assurance your 2013 E450 chassis and our 2007 E350 chassis are identical with regards to relays, but I looked in my 2007 owners manual.  Relay "D" is one of 4 smaller relays.  It is dedicated to Trailer Running Lamps.  To determine if the supporting relay is your problem, place relay "B" (the Horn Relay) into position "D", then replace that fuse again.

Look in your owners manual to relate to what I am describing.  It is a simple test.  The worst that could happen is that relay "B" got damaged during the test, so you would then not have a working horn.

You could also test the original relay "D" by placing it into position "B" and see if the horn works.  Understand that you might have to replace the supporting horn fuse if in-fact that relay is your problem.

We purchased matching fuses and when John put a new one in, it immediately blew.

Any thoughts?

IF that happened with the headlight switch in the off position there’s probably a short in the headlight switch. Here’s the replacement procedure. The cover plate under the steering wheel is easy to unsnap. The trickiest part was prying loose  the corner of the dashboard trim piece after removing the knob and plastic nut.  I replaced mine when the dimmer for the dash lights failed. It’s about a 30 minute job and you can find the switch at Autozone or Oreilly.

https://m.youtube.com/watch?v=SK10M_9i8JQ

IF that happened with the headlight switch in the off position there’s probably a short in the headlight switch.

Oh my!  That is "excellent" input.

The car has been unplugged for a few days while we've been in camp. The second fuse blew as soon as John plugged it in.

 
Which would tell me the Toad is causing the overload.   Which means check the wiring in the Toad from the plug in connector where you attach the wiring from the PC to the Toad (and the cable attaching the PC and the Toad).  Make sure all the wires are clean and properly screwed down or soldered.  Anything that was done to the toad when it was wired to plug into the PC.

Holly,

Has John had a chance yet to dig deeper into this?