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Discussion Starter #1
I am having trouble with a new cargo trailer i just purchased. I have been blowing the M17 fuse in my wrangler. Have traced the possible problem to the running/clearance lights (brown wire). Anyway after trouble shooting, the dealer i purchased trailer from wants me to increase the 15a fuse at location M17 up to a 20a fuse to see if that one blows. He thinks the draw between trailer and jeep may need a larger fuse. I'm extremely hesitant to try, am worried about messing something up in jeep.

Is is safe to try the 20a and see if that helps?
 

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If there is a short or faulty wiring, no matter what you do with the fuse it will blow or cause a wiring failure. How big of a trailer? How many lights are there?
 

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If the thickness of the wire in the Jeep will not support 20 amps then it could damage the Jeeps wiring by switching. If the lights on the trailer are incandescent bulbs then it would be better to change them out for LED trailer lights that draw considerably less current. You can pick them at most autoparts stores and just swap them.
 

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Discussion Starter #4
If there is a short or faulty wiring, no matter what you do with the fuse it will blow or cause a wiring failure. How big of a trailer? How many lights are there?
I do realize that about the short, there is speculation that there isn't a short at all, just the draw from trailer and jeep lights might be higher than 15a, thus a higher fuse. The trailer is just a 5x8 v nose cargo. Has 2 clearance lights up front at top, 3 at rear top, has turns and brakes, thats all. They are all leds.
 

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A specific fuse is rated to protect the wiring. Is there some room engineered in for an increase in capacity, yes. How much, who knows. However, I still would not swap the 15 for a 20. Ask the trailer dealer to provide you with that recommendation in writing that it isn't a problem to swap out the 15 for a 20 to see what happens and I'm sure you'll hear crickets.
 

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The fuse is there to protect the wiring and other components in the circuit. Blowing the fuse means that something is drawing more amperage than has been deemed safe for that circuit, and the fuse serves as the weak link to take one for the team and indicate that there's a problem that needs to be fixed.

A higher amp fuse will allow more current to flow through a circuit that is not designed to handle that much current, and you could potentially damage other components, wiring, or even start a fire.

You need to determine whether there is actually a problem with the running light circuit on the trailer that is drawing excessive current (a short, etc.), or are there just too many running light bulbs on the circuit adding up to too much current?
 

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You need to measure the resistance of the lighting circuit. You can then calculate the theoretical current draw based on 14 V. If it comes out to something like 50-100 amps or higher then you have a wiring fault on the trailer. If it comes in at the 17-25 amp range then you have to cull some lights or have a higher rated circuit added to the Jeep.
 

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Smitty, not that easy. I bulb resistance changes from hot (lit) to cold (off). Easier to look a wattage and go from there. If the bulbs aren't marked it can be looked up based on type.

Sled, listen to what others have said. Putting a larger fuse in does not increase circuit capacity and could be unsafe.
 

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Discussion Starter #9
thanks everyone, i decided no fuse increase. i really had never planned on doing it anyway, just wanted to hear that from everyone else. am still trouble shooting, getting close i think. thanks everyone
 

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Smitty, not that easy. I bulb resistance changes from hot (lit) to cold (off). Easier to look a wattage and go from there. If the bulbs aren't marked it can be looked up based on type.

Sled, listen to what others have said. Putting a larger fuse in does not increase circuit capacity and could be unsafe.
You are correct but in my experience it is either fairly close to the range one would expect or way off. When I check trailers I usually hook the lights directly to a power source and use an ammeter to check the true current flow when in operation. Before I hook it up I check the resistance to make sure I don't have direct short because the light show becomes more than expected :) . Not knowing the OP's experience with electronics I didn't want to recommend using a power source. Yes checking the spec'd wattage of the lamps would be good way of doing the same but I have had some instances with trailers marker lights drawing 5-10 more amps when energized in circuit so I like to do true amperage once I have determined that the circuit is safe to energize. In my experience cheap LED's have less reliable amperage specifications than conventional bulbs.
 

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Speced wattage gets you in the ballpark. Direct measuring is the way to go, like you said, depends on user experience.
Cheap LED's are a scourge, besides being all over the place on ratings, they can be a nasty RFI source, and not always play friendly with CAN BUS systems.
 
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