Pulsating Lights

Brockflock · May 9, 2018

Hi All:

New to the forum. I have a 2005 Sierra Crew Cab with the 5.3 liter engine.

The lights pulsate whenever they are on. They seems worse at lower RPMs, bu they always pulsate some. I just bought this so I have no history, but I do know the alternator is new, and it iss the Bosch style with a two wire lead. The actual model # is a Carquest 11075A. It is a 160 amp alternator, and is considered an exact fit by Carquest.

I have cleaned all of the negative battery connections with emery cloth. All to no avail.

Anyone have any ideas?

Thanks.

Supreme Pizza · May 9, 2018

That is an internally regulated alternator. If your lights are pulsing like that, I would suspect that you have a bad voltage regulator. Its main job is to keep the electrical current even and steady. You could try disconnecting the negative battery terminal while it running, to eliminate the battery as the issue - there is some risk associated with this, as it can cause a spike in voltage. You could also check to see what the lights do with the engine off, if they still flicker when its off - that would eliminate the alternator or engine as the issue.

crankman · May 9, 2018

I had the same problem with a 2008 1500 work truck replaced it with Autozone alternator fixed it up. You may have gotten a bad one from carquest. I had to order mine in from Autozone to get a new one not manufactured.

Supreme Pizza · May 9, 2018

I have seen many alternators and starters test bad right out of the box. On the other had, around 50% of all starters and alternators that are turned in as cores, actually test good. People often change them without properly diagnosing the problem.