Need help on rear running light

I have a problem with the 20amp fuse blowing when I connect my 10’ trailer to my 2551. The running light fuse is ok when the trailer is not attached to my PC. And I’ve tested the trailer with other vehicles and there is no problem with the fuse. But when I connect the trailer to the PC after 15+ minutes the running light fuse will blow. I’m using the OEM PC trailer wiring.

One thing I’ve noticed is the the E450 has a separate fuse for the right trailer signals and another separate fuse for the left trailer signals.  However the running lights for both the rear E450 and trailer  are all on the same E450 fuse? That means that 20 amp fuse is powering a total of 15 combined rear running light on the PC and trailer. That’s a lot lights for one 20 amp fuse even though they are all LEDs.

What am I missing. Is there another fuse for the trailer running lights? I can’t find one in the 2007 E450 OEM booklet. The brake lights, turn signals and flashing lights all work properly. But I have no tear running lights on either the PC or trailer after 15 minutes.

zolman,

It's always problematic trying to troubleshoot a problem (especially electrical) from long distance, but strictly from the symptoms it sounds like you may have identified the problem yourself.
There is likely no fundamental fault in the PC running light circuit if there is never a problem when the trailer isn't attached.  Also, doesn't sound like there is a problem in the trailer circuit if you never experience a problem when the trailer is attached to other vehicles.  Sounds like it is obviously the combination of PC and trailer hookup that generates the problem.

Since you report that the fuse blows some 15+ minutes AFTER you activate the circuit, there is obviously no dead short involved.  It looks exactly like a simple case of excessive current draw for the circuit and fuse involved which eventually blows the fuse.

If I WERE troubleshooting this problem on-site, the best way to confirm the symptoms would be to remove the running light fuse, and insert a DC ammeter (or multi-meter) in line with the circuit at that point to verify that you're drawing in excess of 20 amps.  You could also remove the trailer connection and see exactly what the PC draws through that circuit by itself.  Of course that process would require having a meter that could read in excess of 20 amps (many standard multi-meters only include a 10-amp DC range).

I would think that the OEM circuit and fuse for running lights on any RV would be sized to allow for a trailer or Toad to be included, but simply based on the symptoms you report it sure sounds like you are simply exceeding the circuit capabilities when you add that trailer to the current draw.

Mike

Does your trailer have the typical 4 wire lighting harness?  If so, check for corrosion on where the white wire (ground) attaches to the trailer frame.

The increased resistance from corrosion can cause overloading.

I have a problem with the 20amp fuse blowing when I connect my 10’ trailer to my 2551. The running light fuse is ok when the trailer is not attached to my PC. And I’ve tested the trailer with other vehicles and there is no problem with the fuse. But when I connect the trailer to the PC after 15+ minutes the running light fuse will blow. I’m using the OEM PC trailer wiring.

Curious, does the fuse blow after the lights are on, and vehicle 'at rest' in the driveway after 15 min? Or only underway/in motion?

One thing I’ve noticed is the the E450 has a separate fuse for the right trailer signals and another separate fuse for the left trailer signals.  However the running lights for both the rear E450 and trailer  are all on the same E450 fuse? That means that 20 amp fuse is powering a total of 15 combined rear running light on the PC and trailer. That’s a lot lights for one 20 amp fuse even though they are all LEDs.

Using incandescent, the 'biggest' running light would be the low power filament on an 1157 bulb, at ~8W or ~.6A.  The smaller marker lights (#194) draw ~5W or .3A.  If ALL 15 bulbs were the 1157 incandescent parking lights, you would be at ~10A , or 1/2 that fuse rating. LED is even lower at 1.7W or ~.14A each -  you are not even close to overloading the 20A fuse.  (wattage values rounded up, source https://deepblue.lib.umich.edu/bitstream/handle/2027.42/61187/100985.pdf page 9) 

What am I missing. Is there another fuse for the trailer running lights? I can’t find one in the 2007 E450 OEM booklet. The brake lights, turn signals and flashing lights all work properly. But I have no tear running lights on either the PC or trailer after 15 minutes.

This source - https://fuse-box.info/ford/ford-e-series-2002-2007-fuses-and-relay - shows that there is a fuse for the coach running lights (#10 20A in the under dash panel)  and a trailer running light fuse (#24 20A in the under hood panel)  Which fuse are you replacing? And are you losing ALL the running lights, or just the rear?

NOTE - going out to verify. I found that the numbers on the website diagram for fuse layout do NOT match the under hood sticker. Relay letters are correct. See below-...   



But the fuse number assignments do. WHEW!

In my 2006, I have come to the conclusion that PC wired up the coach rear running lights on the coach to the trailer running light wiring harness and fuse. (#24 underhood, 20A) .  If I pull fuse #10 (underdash, 20A), (diagram and assignment are CORRECT for this box  ) I lose all running lights. If I pull #24 under the hood, I lose only REAR running lights on the coach, and the trailer running lights.    But front markers and running lights work still. This tells me there may be an unused pigtail underneath that has the wires for the COACH tail lights on it, and the PC factory used the trailer pigtail for both the coach and trailer lights.

Same issue with the hazard/turn/tail lights - if the underhood fuse #26 blows, I lose the trailer turn/brake/hazard lights AND the coach REAR turn/brake/hazard. Front turn/hazard still work. My emergency brake module on the trailer was creating some sort of problem that was blowing out the #26 underhood fuse, and causing ALL my rear brake/hazard/turn lights to not work. 3rd brake light still worked, however. That is correctly wired and uses fuse #39 underdash, like the rear coach brake lights are SUPPOSED to.   

So be careful in assuming that PC wired the rear lights correctly 'per factory guidelines'. On my 2006 they obviously did not. With the electric brakes, and breakaway emergency brake module attached, that creates a problem that blows the #26 underhood fuse. Intermittently, and only underway. Like yours, the trailer worked fine with brakes on another truck. I now have the breakaway module disconnected, and have had no issues since on the camper. SOMEDAY I will locate the correct pigtail for the rear lighting and wire it correctly.

Hope this helps a little! 

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Also to save you some time - A resistance in the ground (white) wire would not cause excessive current draw, in our DC voltage system .

 Use the calculator here - https://www.rapidtables.com/calc/electric/watt-volt-amp-calculator.html
Input 12V , and 6 ohms (resistance of a 1157 'high' filament) and press calculate - you get 24 watts, 2 amps. Right on!   

Now lets add some resistance to the circuit from a corroded ground connection, say 10 more ohms. Now WITH the bad connection, our circuit is 16 ohms resistance total. Now reset the calculator, insert 12V and 16 ohms values, and calculate... now there is 9 watts and .75 amps used. You can try higher values, but you will find as the circuit resistance increases the current draw drops, not rises.

What if we REDUCE the resistance, like due to an unwanted grounding in the bulb fixture? Say there is 30 feet of 16ga wire between the fuse and the point in the fixture grounding out. Per this calculator (https://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table) 30 feet of 16ga wire is about .12 ohms. Putting that value in the fist calculator, along with 12v, and you find that the short will attempt to draw 100A (!) and quickly blow the 20A fuse.

So as you can see, adding resistance to a DC circuit like your trailer lights reduces the current drawn, and does not increase it and blow fuses. 

To verify if the problem is a simple "overload" condition, install a 25 or 30 amp fuse.  Once verified, install LED bulbs throughout your trailer lighting to reduce power consumption for a safe permanent solution.  Picking the right LED bulb will reduce power by 90%.  Here is one such example done with my fixtures in the closet, shower, outdoor storage, and Sanicon.

To verify if the problem is a simple "overload" condition, install a 25 or 30 amp fuse.  Once verified, install LED bulbs throughout your trailer lighting to reduce power consumption for a safe permanent solution.  Picking the right LED bulb will reduce power by 90%.  Here is one such example done with my fixtures in the closet, shower, outdoor storage, and Sanicon.

That picture gives a very good example of 'Spherical radiation' light distribution from incandescent bulbs that is missing in many LED bulb designs. Note how the entire housing is lit with the 'old' bulb, and less than 1/2 is with the LED. The light is coming out the end of the LED, similar to a flashlight beam. Unfortunately, the fixture is not designed for that, so much of the 'beam' lights up inside the top, and does not radiate out to illuminate the area. This is a problem especially when turn signals, brake lights and other bulbs are 'upgraded' to LED , while the fixture is designed for incandescent light filaments 'ball of fire' light emitting.

Early automotive LED replacements used 'individual bulb style' LED's clustered in a holder, and were HORRIBLE when used in reflecting fixtures. You can see how the many 'beams' of light all shine one way... no 'Ball of fire' here. But this was the first try with a new technology.


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Later models used 'COB' (Chip On Board) LED emitters, and you can see the distribution of light is a little more omnidirectional. Closer to a 'ball of fire', this type of bulb works much better in a reflective housing than the first style. The early COB emitters were not that bright, so they needed many of them. With all the soldered structure in there, they were/are known for losing working bits also. I wont use these anywhere on a vehicle.

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Here is the 'state of the art' presently for LED replacement for incandescent designed fixtures. COB emitters are much brighter, allowing for just 2 in a bulb. With a hemispherical radiation pattern (HALF a ball of fire ) located in the same spot as the previous filament, they allow for the best illumination in the fixture. Note the large heat sink built in. (These are 1157 replacements, you can see the running and turn LED's side by side. 1.7W and .7w ) (The 1156 'single filament' replacements are 2.3W  )


Yes, they are ''illegal'' for on road use. They put out MORE light than the rules specify.  They work VERY well on my front turn signals, however. 
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For fixtures in the closet, shower, outdoor storage, and Sanicon lighting where the bulb is parallel to the fixture, this style of bulb is fantastic. The COB array rotates, and allows it to shine out the lens without getting 'lost' inside. The array of 'little balls of fire' make for a very diffuse pattern, giving a nice flood light.



I have the Sylvania 1156 LED lights in some of the closet fixtures, and they are TOO bright. (2.3W!!) Blinding. Someday will upgrade to the panel style like these, and re-home the Sylvanias.


So hopefully y'all know a bit more about LED replacement bulbs now, and why some may end up giving less useful light than others. 

Excellent point Volkemon....as well as being mindful of the wattage in your selection.

And now that we all know how neat LED bulbs are, we still don't know HOW his trailer is wired into the RV's circuits.

Does the trailer have a 4 wire or 6/7 wire plug?  If 4 wire, how is it adapted to the PC's wiring?  With an adapter that goes into the PC's trailer wiring socket or was a 4 wire socket added by taping into the PC's trailer harness?  In other words, what is the brown wire on the trailer's harness connected to on the PC?

It should be connected to the tail lights wire on the PC.

And now that we all know how neat LED bulbs are, we still don't know HOW his trailer is wired into the RV's circuits.

Well, at least the LED tutorial was something to read/do while we waited. 

   Heck, we dont even know WHICH fuse is blowing. Or if the vehicle is moving or stationary when it blows...   OP probably found the problem, and no longer needs us.