Rear speaker humming when gauge lights are turned on, aftermarket radio installed
 

Hello all,
I have a 2004 trailblazer, and have recently upgraded the headunit to a new pioneer AVH-110BT. To get past the power problem, I ran two wires to the fuse block from the radio and am drawing power from there. The rear speakers initially did not work at all, and the RSA did not work either, but I took apart the RSA module and connected the input wires from the headunit to the outputs from the RSA for the rear speakers. This allowed me to bypass the RSA controls and get sound directly to the rear speakers from the headunit. All was well until I turned my headlights on and the fuse for the guage lights was blown. I replaced the fuse but then the rear speakers began making a loud humming. After some experimenting I realized that the humming only occurs when the guage lights are switched on, otherwise they operate normally. The humming sounds like some kind of ground loop, but I am no electrician or professional by any means.

Any advice to fix this problem would be appreciated

What do you mean you ran two wires to the fuse box, two positive wires?