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No Power to the #4 pin on my 7-pin trailer plug


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My truck is equipped with the tow package and the 7-pin receptacle for trailer lights/brakes/etc. I have an electric brake controller in the cab. The ground (pin #1), left turn/brake light (#5), tail light (#3), right turn/brake (#6) and electric brake (#2) all work. As I understand it, pin #4 (2 o'clock) is used to charge the battery in the RV trailer. I checked the #4 pin with ignition on & it was dead. I looked at the trailer fuse (40 amp) in the power distribution panel under the hood and it looks good. Where else should I look for the disconnect? Also what is the auxiliary pin (#7, in the center) used for & how is it switched?Appreciate your help,Joe in St Louis

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Re-check the fuse with ohm meter (DVM) I've found several fuses that are cracked and not blown...

Mike, Can't say I've seen a fuse quite like those in the power dist. box before. I tried wiggling it & pulling it out but it didn't seem like it wanted to come out. Am I going about it wrong? Do you know if the power is switched by the ignition? Is there a relay that turns power on to that pin in the plug? Thanks for your help - appreciate your time!
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With the help of Mike's wiring diagram I was able to trace the hot lead from the PDC back to the receptacle, and found a corroded, broken connection. All fixed now - Thanks Mike!The diagram didn't exactly match my '99. I found a pair of connectors behind the left front wheel well; a small one for the truck tail lights and a larger one for the 7 pin trailer receptacle. And my power wire was solid red as opposed to red/orange.Appreciate the help!Joe in St Louis

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