GMC Troubleshooting Questions? Ask a Mechanic for Answers
is this the type of headlight configuration your truck has ?
on the left side 3 prong headlight you should have power on the tan colored wire when the headlights are on and switched to low beam . if not the first thing to do is to check for low beam coming out of the dimmer switch . does your truck have a floor mounted dimmer or column nounted dimmer ?
the floor mount dimmer switches are known for getting corroded in the connector due to moisture on the floor mat / carpet . check the connections there . we were continuously replacing dimmer switch plugs .