Q: Poor charging after replacing alternator - why? 2007 ChevySuburban

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Alternator went out. I bought and installed the new alternator and now all of the lights on the vehicle pulsate when at an idle or driving. Shut the vehicle off but leave the lights on and it stops. I replaced the battery as well. When driving the battery meter on the dash will be at about 14v and drop to 10v and go back to 14v. Is the alternator the problem or is it possible the ecu or the bcu may have been damaged or maybe I've got the belt to tight/loose. I had messed with the tensionor a bit unintentionally when taking the belt off. First alternator job and I messed with the wrong part. It's getting annoying and kind of embarrassing when you're driving at night and people keep flashing their high beams at you because they think I'm flashing them! Haha

My car has 235453 miles.
My car has an automatic transmission.

Hi - I suspect the wavering voltage you describe is either the serpentine belt too loose (tensioner), or the voltage regulator on the new alternator is defective. If the serpentine belt tensioner is loose, it can slip-grab-slip-grab as you describe. Check the belt tension first - a simple, but easy problem to miss. If tension is inadequate, I recommend having the serpentine belt tensioner replaced by mobile, professional mechanic, such as one from YourMechanic, who will come to your location and repair this problem. If the belt tension is fine, I recommend you have a YourMechanic professional examine the charging system for a possible voltage regulator problem.

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