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Trailer Light Fuse in 2004 Chevy Silverado Blows When Any Trailer is Connected to 7-way

Question:

When I connect any trailer to my 2004 Chevy Silverado Truck 7 pin connector, it will blow the 10a fuse located at the drivers side dash. This fuse goes to the left rear trailer brake/trun. I replaced the flasher module. I thought maybe it had a ground on the yellow wire from the 7 pin connector but I cannot find out where this wire terminates at.

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Expert Reply:

Since you have the issue with your truck's trailer left turn fuse blowing no matter what trailer is connected, the issue is likely to be in the truck's 7-way socket or the wiring leading to it. Corrosion can build up in the truck's 7-way socket - either on the pin contacts themselves or even inside the back of the connector - and this can cause two circuits, such as the trailer left turn/brake circuit and the 12V auxiliary trailer power circuit, to become bridged together.

The round U.S. Car vehicle connector that plugs in at the back of your 7-way (such as the Pollak # PK11893 7-way you referenced) can also develop corrosion that can cause circuit bridging upstream of the socket itself.

Either of these corrosion issues could cause a short and blow the fuse. You might want to refer to the linked article on wiring and dielectric grease, which can help prevent wiring corrosion issues. We offer part # LT37534 for protecting and preserving solid electrical connections. Look for any wires that have bare metal exposed and repair as needed.

I suggest you disconnect the round connector from the back of the 7-way and inspect it and the 7-way. Clean with an aerosol contact cleaner and a small nylon brush - avoid using metal brushes as these could leave a stray metal strand that itself could cause a similar issue. Most auto and electrical stores will carry an aerosol contact cleaner. Sometimes even just trapped moisture or dirt within the connector can cause a short. Once cleaned, apply dielectric grease.

If you have a circuit tester like # PTW2993 you can test the truck socket functions without the trailer connected. If you refer to the linked photo of a 7-way, you'll see the common pin/function configuration. Usually, the ground wire is made of white, and the yellow wire carries the left turn/stop signal. You can apply the grounded tester to each circuit on the 7-way, one at a time while a helper activates each vehicle function in the truck, to see if those functions operate properly without a trailer connected.

I also suggest making sure the 10-amp fuse is the correct value for the left turn/stop circuit.

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