2005 GMC Sierra 2500hd
4L80e automatic transmission
170,000 miles
I turned the dome light off and unplugged everything from the cigarette lighter and checked for parasitic draw and there was nothing. Everything was off when the truck was locked.
Have you checked the battery itself? Also the alternator?
Depending on the battery type, I would make sure none of the cells need water as well.
Can’t add water to this kind of battery.
Is the battery reading good when you check it? No loose connections at the terminals or any corrosion?
Battery tested good and terminals are tight. And I’ll check for corrosion.
If your alternator is charging at about 14 volts at idle, you probably have a dead cell in the battery.
Charging is normal.
Well, this might seem a bit too obvious, but it's worth asking. Any corrosion on the terminals? The clamps on the posts? Intermittently bad wires coming out from the clamps? Are the clamps not tight enough?
You could replace the clamps and wire harness, clean those terminals, and see if that helps.
Does the battery still die if you disconnect it at night?
Nope. I’m thinking it’s the instrument cluster because the mileage and prndl keep flickering on and off.
might be a dodgy ignition switch. I think you should find a wiring diagram.