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Discussion Starter #1
I have one low-beam headlamp (right-side) which is noticeably less-bright than the other (2009 CC, I-5 SLE-2). The bulbs are Sylvania halogens, the same # and grade, purchased together, they're not 'mix & match' different bulbs. I am guessing this is due to a possible bad ground in that low-beam circuit. No other bulbs are affected, no turn signals/brake lights/running lights, etc. Switching the bulb from the affected side shows it to be functioning correctly when installed on the opposite headlamp circuit.

An inspection of the plug doesn't show any noticeable corrosion. The wire into the plug doesn't appear to have any broken strands causing that type of problem. The fuse is good for the circuit. Is there a body ground for the circuit for each headlamp that I need to check? I think that if there was a single ground both sides would be affected but that is not the case. I checked the Rshadd sticky for the wiring diagram but I don't see a ground for the light, I see where one lead goes into the relay (orange lead going to the relay #30 terminal). The other (dark blue?) goes to terminal #87A of the Beam SEL relay. Thanks for any assistance.
 

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The ground wires for both low beams meet at pin F5 in connector X1 in the fuse box. Then the circuit goes in at terminal 87A and out terminal 30 of the Beam Select Relay. The ground side of the circuit ends at G105, which is the ground splice pack on the left fender wall, aft of the battery. There doesn't appear to be any splices or connectors between the lights and the fuse box.
 

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Discussion Starter #3 (Edited)
Thank-you!

Latest post:
My Homestead FL neighbor who shared his electrical schematics w/me helped me to track-down a break in the circuit and fix it. Now I can see as you ought to be able to, at-night. Best of-all, no dealership bill.
 
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