05 Subaru Legacy 1 low beam much dimmer than the other.

[Lunchbox44]

05 Subaru Legacy has the passenger low beam very dim, all other lights and functions work as they should. I have replaced bulbs, checked and replaced fuses with no change. I have read alot about it being a bad ground. I have ran a direct wire from battery negative to the bulb, no change. I also tried another wire from positive battery to the bulb, no change. Is it possible the low beam reflector could be bad inside headlight housing?

 

[Ecmbuster]

Check and clean the ground connection to that light.
Clean all the other grounds you see from the battery negative to the body, battery negative to the engine block and any ground straps that are known or visible

 

[Lunchbox44]

If you install a direct wire from battery negative to the negative of the bulb, doesn't that give a direct ground and bypass anything that could be bad connections? I tried this with no changes to the brightness.

 

[Ecmbuster]

Then check the positive side but you will need a schematic to chase the circuit backwards to the power source.
You can test the voltage drop on the positive side.
https://gearsmagazine.com/magazine/let-your-voltmeter-do-the-math-during-routine-voltage-drop-test/

I use the Load Pro and it calculates the voltage drop at each connection point with the meter.
Great future tool.
https://www.aeswave.com/LOADpro-48v-Dynamic-Test-Leads-p9579.html

The correct model gets the correct wiring schematic as in the image.