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Discussion Starter · #1 ·
2004 6.0L Diesel Excursion.
I have been pulling a trailer for 6 years with this excursion. Last week the running light 20a fuse under the dash started blowing when I hook a trailer with either a 4 or 7 pin connection. The brake lights, turn signals work. Today with the trailer hooked I put in 20a, 25a, and 30a fuse. All blown.
I do not have an owner books. I have found 2 little fuse boxes under the hood but I haven't found any blown fuses (mostly they are the square black relays and I don;t know how to check them and not fuses)
 

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Have you tried testing the circuit with a different trailer or just a test light to see if that blows the fuse?
Does the fuse blow with out the trailer?
 

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Check your ground wire on the truck and the trailer both - they are kind of flimsy and do all kinds of weird stuff if they aren't getting a good connection. Do not add in a higher amp fuse. Fuses are there to blow if there's an electrical problem, if you put higher amp fuses in and are getting a lot of juice that you shouldn't be, it can cause an electrical fire.

Are you using the regular 7 pin or 4 pin or with adapters?

Relay box (under the hood)



The little fuse box under the hood is for trailer relays, I'd check those.

How to test relays:

I would imagine you can ohm them out too.
 

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Discussion Starter · #4 ·
I can not find that fuse box under the hood. I don't know how to up load a picture on this website or I would show you what is under my hood.

I am using a 7 pin plug. I cleaned both sides of the plug with electric connector cleaner. Anyway tested the output at the truck side plug. Everything works without a problem. When I hook up to the trailer the fuse blows in about 5 seconds. Brake, turn signals and flashers all work before and after the plug blows. Checked the ground on the trailer as far as I could (the bottom is enclosed) and it was good. Also good on the truck side from the hitch to the under the hood.
 

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So the problem is the trailer. Either a bad bulb or hot wire shorted to ground.
 

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^I'll second that.
 
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