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Can Grounding Issues Affect Lighting and Trailer Brake Functions on 2001 GMC Sierra 2500 HD

Question:

Hardwired an LED Firestrip to my Auxiliary trailer lights port on my truck. Now when I plug in my trailer lights, my left turn signal causes my right turn signal to also pulse on my trailer. I also get an Error on my trailer brake controller now too. Could this be because my trailer lights are incandescent? I am positive the Firestrip is wired properly Left turn, Right turn, Brake, and Ground. Wiring Diagram Incoming Auxiliary Power []Auxiliary Trailer port Firestrip. I also had an amp installed for speakers, could this be a grounding issue caused by the amp?

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Expert Reply:

Your recently installed audio amplifier should have no interaction with the vehicle or trailer lighting since it should be directly connected only to the battery +12V and ground. There should be no common wiring between the audio and lighting systems. Your trailer lights being incandescent should have no bearings on this issue.

What is the error message on your trailer brake controller? If it indicates that it has lost connection to the trailer brake circuit then there could be a corrosion issue within the connectors or a bad ground on the truck or trailer harness.

A loose or corroded main ground connection can cause all sorts of issues with trailer lighting, including weird behavior like what you describe. I suggest making your first step a check of the main ground wires for the truck's and trailer's harnesses. These ground connections need to be made to a clean bare metal surface, free of rust, grease, paint, primer, etc. Try sanding off the ground points on the truck and trailer frames and re-connecting the ground wire ring terminals. Dielectric grease like # 11755 helps protect those new clean connections.

Also check all wiring connectors for signs of discoloration or corrosion. Sometimes corrosion will develop inside a connector housing where it can be hard to spot. This issue can easily cause shorts between adjacent circuits that could lead to issues.

If the grounds and connectors are okay I suggest disconnecting the light strip and testing the trailer light and brake functions again.

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