Overcharging issue new alternator same problem what else should I check

Gather App
M

maxtowmode25

Member
Joined
Jun 30, 2025
Messages
6
Okay, so my truck's been acting up lately. First, the headlights flickered and the battery light showed up. I thought it was just the old battery, so I replaced it.

The next day, the radio went silent and the battery light was back. A scan showed the alternator was giving 16.3v. A shop agreed it was overcharging, so I put in a new one. But the same problem remains: the battery light's on, and the voltage hangs around 16v.

I even tried unplugging the smart charge thing, but no luck. Another test showed the voltage regulator in the new alternator is already broken. The shop thinks it could be a wire or ground issue.

What should I check before I ruin another alternator? Any tips or similar stories would be great.
 
That much juice sounds like bad ground or a wiring fault feeding the voltage regulator. If I were you, I would check the grounds between the engine, frame, and the battery real good.
 
Modern "smart charge" systems are often more trouble than they're worth, adding unnecessary complexity that leads to fried alternators and endless electrical gremlins when a simple regulator used to do the job just fine
 
The whole smart charging system is more of a liability than a feature, overcomplicating basic electrical systems with software just makes modern trucks unreliable and harder to diagnose. Sometimes, old-school simplicity beats tech-driven efficiency every time
 
maxtowmode25 said:
Okay, so my truck's been acting up lately. First, the headlights flickered and the battery light showed up. I thought it was just the old battery, so I replaced it.

The next day, the radio went silent and the battery light was back. A scan showed the alternator was giving 16.3v. A shop agreed it was overcharging, so I put in a new one. But the same problem remains: the battery light's on, and the voltage hangs around 16v.

I even tried unplugging the smart charge thing, but no luck. Another test showed the voltage regulator in the new alternator is already broken. The shop thinks it could be a wire or ground issue.

What should I check before I ruin another alternator? Any tips or similar stories would be great.
Click to expand...
Yeah, 16V is definitely way too high and will fry a battery and anything else connected!
And yeah, it could be a wiring or ground issue.
The BCM controls the alternator output on these trucks, and if it's getting a bad signal from a corroded wire or loose ground, it can tell the alternator to crank out too much voltage.
I'd start by checking the main ground strap from the battery to the chassis, and the one from the engine block to the chassis.
Also take a close look at the small wire harness that plugs into the back of the alternator and make sure all those pins are clean and the connector is solid.
You can be lucky with just cleaning up the terminals and grounds, but a faulty BCM isn't out of the question either.
It's an expensive part though, so I'd exhaust all the wiring checks first!
 
Bad ground or corroded connection can make the regulator go nuts and cook itself and also yh I've seen cases where a chafed harness near the alt caused the same 16v issue.
 
Take a multimeter and put one lead in the ground terminal on the battery and one on the engine block or even on the alternator mount, start the engine and see what reading you get, shouldn't be any above 0.5v should be 0.0v for a perfect ground. Try with lights and heater running full blast to create load. You can do the same on the positive battery post and the positive feed from the alternator. Could also have high resistance in the positive side.
 

Latest posts

Back
Top