Headlights flicker when brake pedal is pressed

[gearhead572]

Ive got a bit of a electical gremlin in my truck. On my 08 gmc sierra 1500 wt I noticed my headlights flicker for a breif second but stay on.

 

Ive had the bcm changed for other reasons, alternator replaced because of a bad diode, fuse panel replaced due to corrosion somehow, and the brake pedal switch replaced. Ive had the pcm scanned at the dealer to see if its had any codes stored in it, nothing.

 

The only other thing I can think of is a bad ground maybe. The headlights are the only thing ive noticed that flickers. The dash lights are fine and dont seem to flicker.

 

Could it be the wiring from the brake controller that the previous owner installed?

 

I need help here. I do lots of driving in the early morning and night. Its driving me insane when they flicker lol

[POS VETT]

Do you have LED bulbs in the brake lights?

[gearhead572]

No I don't have any LED bulbs in the brake lights.

[intheburbs]

Do the lights flicker with any other electrical load? What if you crank the blower on high, hit the rear defrost, or hit all the power windows at the same time?

[gearhead572]

Its a work truck edition. Manual crank windows and door locks. No actuartors of any kind. Only the headlights flicker nothing else.

 

It doesnt matter if the blower is on high, high beams are on, interior lights are on, stereo is cranked, and the sirius radio is plugged in or if i sit and idle. Hit the pedal and theres a flicker.

 

I noticed tonight that when i idle with the highbeams on and nothing else they would go slightly brighter and then dim back to normal. What the hell is going on here?

 

Would it be the PCM not regulating the voltage properly?

 

I know that pretty much all newer vechiles dont have voltage regs in the alternators. Its regulated by the PCM or the ECM.

[2005LT]

Hi Gearhead, I have what I believe to be the same thing as you on my 2009 1500. I would characterize it as more of a brief "dimming" of the headlights....maybe 1/2 a second long. After that, they come back to full brightness whether still on the brakes or not. I just got used to it and it hasn't caused any other effects.

 

From what I remember (going back years now on this forum)....I thought I read something about the brake booster causing the momentary increased power draw on the electrical system....or at least that lighting circuit. I could be wrong though.

[gearhead572]

Iam determined to find out whats causing this. Most of the time it flickers, other times its a really breif dimming.

[gearhead572]

I dont get it. I work at a auto parts store. I grabbed a LED kit off the shelf for the highbeams because its plug and play and installed them. Drove home tonight and not a single flicker or dimming of the headlights when i pressed the brake pedal.

 

Could the visionX bulbs be the problem?

BrightSource LED kits are nice and bright