Dim headlights

2006 CTS base,3.6, non-HID headlights. The right (passenger) side headlights (high and low) are very dim (just noticed yesterday). I have checked both hi and lo fuses and the same relay controls both sides of the vehicle. I suspect I have a faulty ground to the sockets. The wiring diagram in my Haynes manual shows both sockets going to ground. Does any one know if the sockets are grounded with a lug to the chassis and, if so, where is the lug? In other words, how much of the front of my car must be removed to access the wiring? Thanks.

Forgot to mention that the problem only happened in the rain. Took the bumper cover off and discovered that some yutz had replaced the turn signal light socket and used butt connectors to splice the new socket in. After a proper wiring connection (solder and heat shrink) and a rainy day (FINALLY!) all seems to be good.

Thanks for the update. As you discovered, unsealed crimp connectors are almost never a good idea.