Marker clearance lights blows Nissan titan 10 amp fuse

[p barker]

When I plugin my Wildwood, towing cable into my truck, blows 10 amp fuse in truck every time it’s a direct short ,I had tested towing cable bycompletely cutting it out and putting 12 Volts Viva jumper wire to white clearance wire and negative to green ground Wires arcs no lights come on over the entire trailer can anybody give me some help? I have checked all the lower clearance lights and looked for white and green wires to see if they were pinched, looked underneath where wires go into barrier didn’t see. Any pinched wires,haven’t tested the upper clearance lights yet I have to get on the ladder to do that , truck does not blow fuses when not hooked up to RV.

[Chuck_S]

You got the right fuse in there? A ten (10) amp fuse to the trailer lights? As near as I can tell there's a 25a (twenty five amp) fuse for trailer running lights in my Ford Expedition's fuse box.

-- Chuck

[TitanMike]

Originally Posted by Chuck_S

You got the right fuse in there? A ten (10) amp fuse to the trailer lights? As near as I can tell there's a 25a (twenty five amp) fuse for trailer running lights in my Ford Expedition's fuse box.

-- Chuck

Nissan put two separate 10 amp fuses in to protect the body control module (BCM). Lots of issues when people plugged in trailers with shorted brake and tail/clearance light wires. Was a recall on my first year 2004 Titan. The fuse blows when there is a short somewhere between trailer umbilical cord plug and liights.

Upping the fuse size just risks damaging the BCM which will cost $400-600 depending on year/model plus labor.

[p barker]

The ten amp fuses for clearance lights only. It’s been in there for five years. Haven’t had any problems with it. Even when I took it out the last time it’s been parked for six months hooked up to try to get the state inspection in that happened. Nissan has separate fuses for turn signals brakes and clearance and relays. This is a titan with a diesel. There’s no problem with the truck. This fuse is strong enough.

[aircommuter]

I think that is going to be old fashioned inspection by flashlight and crawling around. I would start with the ground, see if each light is separately grounded or through the frame. If you can’t see the problem and wires go through structural members then you may have to cut and connect a wire to the one in question and pull it out so you can inspect.

[TitanMike]

Originally Posted by aircommuter

I think that is going to be old fashioned inspection by flashlight and crawling around. I would start with the ground, see if each light is separately grounded or through the frame. If you can’t see the problem and wires go through structural members then you may have to cut and connect a wire to the one in question and pull it out so you can inspect.

My first targets would be the umbilical cord plug if not one that's molded to the cord. Could be shorted connections inside. Also the junction box where the umbilical cord joins the trailer's lighting wiring.

One way to more isolate the problem would be to disconnect the light wires in the junction box ( leave12v +, ground, brake, wires connected-) and plug cord into truck.

If fuse doesn't blow the cord is OK.

Now check wires to lights with ohm meter for resistance to ground. One with zero ohms is shorted somewhere.

[Aussieguy]

on a standard plug

white is the ground ... to trailer frame
light green is the reversing lights
dark green brake lights and right turn

[p barker]

Thank all of y’all for the replies, I am a retired mechanic work for the rental industry in the field. I have tested the umbilical cord it’s working fine. I actually cut the wires in the junction box, put 12v the white wire with power and jump the green wire as nd grounded it by jut touching it was shorting out, I’ve checked all the clearance lights on the bottom the next step was what you said at the last would be to ohm out all the wiring after I checked the clearance lights on the top of the RV it’s a 42 footer I’ll have to get a ladder to get up there I will probably do that next week

[firephighter]

Originally Posted by Aussieguy

on a standard plug

white is the ground ... to trailer frame
light green is the reversing lights
dark green brake lights and right turn

This is what I thought reading the first post. Then, has it been working this way all along? I would have to verify wiring before I started chasing other avenues.

[Aussieguy]

Originally Posted by p barker

When I plugin my Wildwood, towing cable into my truck, blows 10 amp fuse in truck every time it’s a direct short ,I had tested towing cable bycompletely cutting it out and putting 12 Volts Viva jumper wire to white clearance wire and negative to green ground Wires arcs no lights come on over the entire trailer can anybody give me some help? I have checked all the lower clearance lights and looked for white and green wires to see if they were pinched, looked underneath where wires go into barrier didn’t see. Any pinched wires,haven’t tested the upper clearance lights yet I have to get on the ladder to do that , truck does not blow fuses when not hooked up to RV.

the way I read this is the OP is shorting out the wires

all the colored wires are positives


EXCEPT for WHITE, which is the negative and is connected straight to the frame


putting 12v to white will arc and blow fuse
putting green(s) to FRAME will arc and blow fuses.

[Chuck_S]

12v DC house wire colors are different from 120vAC house wiring colors. As noted White is ground in a 12vDC "house" (AKA trailer). Trailer batteries are frequently wired "backwards" although I'm not sure that's relavant here.

Assuming the battery is wired properly the trailer lights can be tested by jumpering Pin 4 (+12vDC) to the pins for the lights on the umbilical cord. Pins 4 and 3 should illuminate the running and tail lights. Use a fused jumper for safety against short circuits. (This jumper is frequently used to illuminate the trailer exterior on campsites.) If the fuse blows there's a short in that system.



-- Chuck

[p barker]

Not on the forest river fifth wheel. The wire white is 12 volts pos to all clearance lights the green is the ground colors power and negatives as I stated.

[cyclenate]

I had a friend with a new trailer...on the 3rd time out, they had the same problem. We found the middle upper running light was shorted. In fact, the wires were melted. You will need silicone sealant after re-installing the plastic orange running light.

[Aussieguy]

could not find any information on different wiring connections from tow vehicle to a 5th wheel is any different than any other travel trailer
they all appear to use the same color coded wires

Don't mix the trailer lights and brakes wiring harness, with the house 12v harness. Colors for the HOUSE will be at the builder's discretion
the aux power from truck goes to the house battery.

It may be possible you are looking at the light fitting...?
someone may have wired the fitting's pigtail so the green is going to ground
usually this won't affect the light's performance BUT it makes it look like the colored wire is NEGATIVE

your best bet is to use a multimeter set to ohms and check the 7pin plug on the trailer


attach one probe to a good connection to frame
use the other probe to measure each pin in the trailer plug
only ONE wire in the plug should read zero resistance (0.00) should be white

all the rest of the pins will have some small value or meter will read OL


it is possible you trailer was re-wired by someone?