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Old Fart
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889 Posts
Discussion Starter #1
I have a 2004 F-350 diesel truck that I bought new. I have added two items that are in the tail light circuit; clearance cab lights and a rear stop/tail lightbar. 5 or 6 months ago I noticed the tail lights were not working. I checked the fuse and it was blown. I changed out the fuse (10 amp) and turned on the lights. The fuse blew immediately. I removed the headliner from the cab and checked the wiring to the cab lights. It is perfect and not nicked or cut or chaffed. I used the factory harness when I put in the cab lights. I did the fuse thing again and it still blew. I remover the rear light bar and checked it again, and it still blows the fuse. I have crawled under the truck and looked for animal chewing marks, cuts and shorts; nothing. I am not a hack when it comes to wiring, I can build computers and radios, using the radio shack kits of the old days (wired and no circuit boards) I have wired several Jeeps in the past, so I know something about how vehicles are wired. DOes anyone here have any ideas? Thanks.
 

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Senior Member
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1,324 Posts
I was thinking maybe the trailer plug circuit but it has its own fuse per the manual. Start pulling bulbs maybe one of the holders shorted out? Get a good supply of fuses first!
 

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Old Fart
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889 Posts
Discussion Starter #3
Thanks Weld. I did the trailer plugs and they were good. I pulled the lights out of every socket of the truck and all were good and clean. No shorts that I could see. I can't use an ohme meter as there is a short to ground in the harness somewhere. I could pull out every socket on the truck. That will take time, but doable. I will up plug each light assy and look for the short that way. NONE of the lights have ever been messed with by anyone but me. I have not spliced any wires in the truck. I have only used plug in sockets. No soldering or electrical tape.
 

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Senior Member
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3,051 Posts
Dave,

Isolating-disconnecting each pathway one at a time that the 10A fuse powers up will lead you to the short. A portable circuit breaker can be used instead of the fuse when trying to locate a short.

Could be something in the light switch itself too.

I'll make a note to myself and check if any worthwhile wiring diagram is available on alldata at work tomorrow.

Harry
 

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Old Fart
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889 Posts
Discussion Starter #5
Thanks Harry. I have the wiring diagrams from Ford for this truck. The circuit breaker is a good idea. I am going through fuses fast. They are 15 amp and not 10 amp like I stated in my first post. The headlight switch might be it. I have never had one short out. I will look at it on Wednesday.
 

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3,051 Posts
Dave, I just got to work and found this recall listed about the multi function switch being defective and causing loss of any combination of the...turn signal lights...brake lights...tail lights...hazard lights.

the recall no is...11C18110708-001

its the turn signal switch that they are talking about that can have a short inside of it

I printed the entire recall info and will provide more details when I get home this evening, have to fix some cars right now.

Harry
 

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Old Fart
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889 Posts
Discussion Starter #7

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Senior Member
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After I read the entire recall, it say's our SuperDuty trucks are included, but only if the turn signal switch had been previously replaced between 1-12-11 through 4-9-11...so in other words it was a bad batch of replacement parts (multi function turn signal switches) in a narrow time frame.

Harry
 

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Old Fart
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889 Posts
Discussion Starter #9
Thanks Harry. That is what I figured. I ordered the Headlight switch. It will be here in a couple of days. Ford of Ukiah doesn't seem to stock anything I need for this truck...
 

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Old Fart
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889 Posts
Discussion Starter #10
Well Harry, the new headlight switch did NOT work. Still blows the fuse. I am going to isolate each light by removing each bulb, one at a time. I was disappointed when the switch did not work.
 

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Wish I could be there to help Dave. Need to start disconnecting any circuits involved with that fuse so as to isolate the direction to follow towards the short.

Harry
 

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Old Fart
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889 Posts
Discussion Starter #12
I disconnected all of the lights and tried it, no joy. Now I will have to get under the truck and start to disconnect the harnesses from the furthest, to the the switch. This won't happen until mid of next week.
 

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Old Fart
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889 Posts
Discussion Starter #13
I fix it. When I removed each circuit form that fuse, I missed the CORRECT clearance light circuit. Today I hooked a circuit breaker into the fuse position and turned on the lights and discovered that I had one clearance light out. I changed the bulb and everything works. I am guessing that the bulb went out and caused a short with in the bulb (which I have never seen). It looked normal to me. Thanks for the help Harry. :clap :cheerleader
 
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