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Old 12-06-2012, 02:50 PM   #1
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crazy brake light fuse issue

I know there are a few topics on this already but mine is a weird one that i havent seen before and its driving me crazy. I have a 2003 Fleetwood Discover with trailer brakes and a enclosed trailer. When I plug my trailer into my rv and press the brakes the brake light fuse blows instantly. My rv brake lights work fine when the trailer is not plugged in and the trailer works fine when its plugged into my truck. So i know the trailer wiring is right. I tried taking apart the tow plug on my rv and all the wiring looks fine. I tried unplugging the trailer brake controller to see if it was shorted and then stepping on the brakes but it still blows the fuse. When i bought the motorhome 2 years ago and brought it home the fuse was blown so i know the original owner probably had the same problem. I also found one of those towing power modules that was connected to the towing wiring so i tried bypassing that but it didnt change anything. I ran out of solutions so can anyone help me with any more things i can check? thanks

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Old 12-06-2012, 03:51 PM   #2
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What is the amperage of the fuse? Perhaps you are asking the circuit to power too much. Is the brake controller wired properly? A meter and some troubleshooting is needed. Does the fuse blow if the trailer light bulbs are removed? then you know its the brake circuit. If the brakes are disconnected, do the lights blow the fuse? These answers can help pinpoint the problem.


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Old 12-06-2012, 05:54 PM   #3
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Had a turck several years ago that was blowing fuses when I would hook up the trailer. Turns out that I had a pinched wire that was cause the problem. Re did the wiring and the issue went away.
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Old 12-06-2012, 05:55 PM   #4
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Since you are sure the RV plug is wired correctly and is corrosion free, I would recommend you follow the wiring from the RV plug as far as you can. In my 97 Discovery there was a white plastic plug that the RV plug wiring went through somewhere buried behind the rear cap. I don't remember the exact location. This plug on mine was severely corroded causing all sorts of shorting problems until I found the plug and cut the plug out of the wiring and joining the wires directly to their mate. I remember was corrosion even in the individual wires for several inches in either direction of the white plastic plug.

Hopes this helps in some way.
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Old 12-06-2012, 07:36 PM   #5
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Have you checked if it is indeed wired for trailer brakes and not a tote. Electric brakes require a lot more power.
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Old 12-06-2012, 10:25 PM   #6
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Years and years ago one of the first supercomputers in the Pentagon wouldn't give reliable results. When they called in the repair people it worked fine. Over and over, same thing. Spent a bunch.

One bright guy found a burr on a door. When open, when the repairmen were there, it was fine. Close the door and go home, the burr shorted out one of the circuits.
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Old 12-07-2012, 12:55 AM   #7
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question, does your tail lights on MH have a yellow lens on the top? If so, there is a five to four wire diode box somewere between the tail lights in MH and the 7 pin plug. My 02 discovery has this and that diode box has caused more agravation
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Old 12-07-2012, 09:16 AM   #8
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Thanks for all the reply's guys. It has a 20amp fuse and i tried a 30 amp one time just to see and that one blew right away also so its gotta be a direct short somewhere. Brake lights have a seperate fuse so the running lights and turn signals still work after the fuse blows. The only thing i tried with the trailer brakes was unplug it at the main controller in the drivers seat area and tried it again but it blew the fuse. Yes i do have the yellow lense that makes the turn signal a seperate light from the brake light and i found that diode box which is called a roadmaster brite-lite (http://www.etrailer.com/Accessories-and-Parts/Roadmaster/RM-732.html) I thought that might of went bad so i bypassed it to see but it still blew the fuse. 7 times out of 10 I spend a whole day on a project just to find the problem was something obvious i overlooked that would of been a 5 minute fix so i figured I'd see if i was missing anything before i went all in. I guess I'll grab my meter and go to work on the wiring this weekend and try to find the problem. I'll let you guys know what i find. thanks again
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Old 12-07-2012, 10:05 AM   #9
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You said you 'bypassed' the trailer wire module, but did you completely disconnect it?

I've seen them go bad before, when they do they do some pretty funny things.

Also, is the trailer wiring converter powered by a switched lead off the ignition, or by the brake wiring itself? If it's powered by the brake light lead the surge as it starts up under load may be significant.
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Old 12-07-2012, 10:32 AM   #10
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Just because the tow vehicles lights operate correctly when not towing doesn't mean the wiring is right to the 7 way connector. Look in the most obvious places like the connections between the tow vehicle and trailer first. look here: http://www.google.com/imgres?hl=en&c...9,r:2,s:0,i:92

Take your 7 way connections apart and see that the pins are wired correctly with a volt meter between the pins and ground on the tow vehicle.Use an ohm reading on the trailer to look for shorts and then use a battery to check all trailer lights. My guess is you have a brake wire shorting to ground through the connector or they are badly corroded causing weird shorts and other problems. Take both sides apart and check wiring. If all is good in the trailer and tow vehicle 7 way connector, scour the trailers wiring for a short.
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Old 12-07-2012, 06:41 PM   #11
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Check and see if the pin in the middle of the MH side is a hot wire or ground. I think I read somewhere that if a hot wire was needed to charge the battery in the toad that was used. And it may have to be a ground . Or it's a ground on the trailer side, which , if the MH side is hot that won't work. Does the trailer brake and all the lights go thru that plug? You should be able to check the plug with a test light. Just compare it to your truck.
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Old 12-08-2012, 04:42 PM   #12
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the wire module is connected directly from the brake wire but i did completely disconnect it from the wiring. I didnt want to say it on my first post because it would of made things more confusing but when i first disconnected and bypassed the wiring module and hooked the trailer up to the MH in the driveway the brake lights work fine on both the MH and the trailer so i thought i figured it out but when i pulled the MH out the next week for our trip it magically blew the fuse again and i didnt change anything from the week before which confused me even more. I also hooked the MH up to a different trailer so i could test it and it did the same thing and blew the fuse. The trailer i have is brand new and as i stated before it works perfectly when I'm towing it with my truck so i doubt its on the trailer side. Im gonna take the MH side plug apart again and test everything for sorts and to see if it matches the trailer side like Paul and jeepfreak are suggesting and go from there. The kids are sick as dogs today so I'm playing doctor. Hopefully I'll have time to get out there tomorrow. thanks again
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Old 12-08-2012, 05:43 PM   #13
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Make sure you let us know what you find. With you latest post, I'm still leaning toward a corrosion problem giving you the intermittent problem. You have me as curious as a cat right now.
Good Luck, Be Safe and Above All, Don't Forget To Have Fun
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Old 12-08-2012, 07:39 PM   #14
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The wiring diagram for the Brite-lite converter shows that you need diodes on the trailer side of the 4 way plug.

Never Mind- Just found the instructions, diodes are needed for a car in tow not a trailer.

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brake, fuse

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