Electrical/lighting problems

I'm the original owner of a 2001 Yukon XL with only 40k. Recently I've been having problems with the headlights and day-lights not working. The dealer said it was the battery cables, which I switched out. I also purchased a new gel battery. Sometimes the day-lights will not work, and at times, when the vehicle switches from day-lights to headlights, the headlights will not work. Even if I turn them on manually, they will not come on. The brights will work, but that's it. Also, the interior dash lights flicker on and off. Could it be the headlight switch? The photosensor? I've also switched out the fuses. I just got it back from the dealer and it's at it again! Anyone have any ideas!?!?

Hi,
here is the flow if you turn on the headlamp manually:
Junction Block - Underhood 10A fuse to Headlamp Switch to Headlamp Relay to 2x 15A fuse to 2x Headlamp - Low Beam and High Beam. Then to the Headlamp Dimmer Switch to ground for either high or low beams.
The Ambient Light Sensor feeds the Body Control Module (BCM) and then it goes to the relay.

In both scenarios you go through the headlamp switch and the relay and the headlamp dimmer switch. The fault may be upstream of the headlamp switch before the 10A fuse.

The cheapest step would be the relay, after that the switches, neither may be the problem.
Can you check the 10A fuse when it does not work? Could be a bad contact or wire somewhere.
Take care, Eggert :bananasmi

I have the same problem. Highbeams work but not the low. Changed the switch and still have the same problem ($60 later).