Headlights flicker almost like strobe lights

have battery load and voltage tested and check that voltage output of alternator is adequate while engine is running with headlights on

you need to run another cable to frame of car or fix existing one you have a bad ground to chassis

you forgot, does it do that running engine or not.?
ok the main battery is car is doing that.
use a voltmeter, at the battery or even at the CIG lighter port.
12.6v DC, not running. rested. running voltage is 13.3v to 15vdc,

start engine, is rpm above 800 RPM at all times, or more?
if not, the alternator will be too slow, and drop out and when that happens , the lamps will dim. (a 3 volt drop does that)
1: all fuses good
2: battery term lugs clean, not green
3: fan belt to alternator not loose. slipping.
4: charge lamp on dash not ON, running.
5: check engine lamp not on, running (if yes,scan it now)
6: test the battery , batteries are LOW life objects, (die-easy-not-hard)
test the battery , using a load tester or take it in for testing, it's free.
or try a spare battery from another car. do not reverse POLARITY.
this gets the lions share.

Replace your breaker in the breaker box, and I wouldn't use these lights till its fixed. Kill the lights, kick the breaker to the off position This is the first thing that happens before an electrical house fire.

Relay may be crapping out. Try swapping it for another relay in the box.

Are you having problems with headlights or interior lights flickering or dimming for no apparent reason? You are not alone! Many other consumers have reported experiencing the exact same problem. The problem is seen in many different GM makes and models including, but not limited to: Chevy Suburban, Tahoe, Silverado, Corvette, Camaro, Firebird and Malibu's and Pontiac Aztek's.
Why Are My Headlights Flickering?The headlight flickering or dimming may be caused by a intermittent low voltage output from engine vibrations. When this occurs, a voltage spike causes the voltage regulator to reset. During the reset, generator output drops to almost zero. This is a known issue with GM cars and the correction involves replacing the alternator. Would recommend seeing dealer for proper alternator application to resolve concerns. Probably has a superceded part number to indicate internal changes.

check your switch!!

I just had this problem. There was a screw loose on the hi-beam switch. You have to take off the plastic cover on the steering column to get to it. Really simple to fix yourself (5 minutes tops). 4 screws and the turn of a small wrench. Free if you do it yourself, $600 if you take it to the dealer.

have the charging system tested when this is happening, also have the battery tested, any Autozone or Kragen will do this for free.

the inner lights are the brights but some vehicles also use the bright lamps with low voltage as the daytime running lights