I ran a wire for an amplifier yesterday. The battery was disconnected while doing this. I removed the passenger side floor fuse box since I needed room to get the wire through the firewall. After putting the fuse box back, double checking all the connections and connecting the battery the truck won't turn on.
When the battery is connected the headlights turn on for a second and then turn off. When I push the start button the truck clicks once and then nothing. Pushing the start button again does not lead to more clicks. Power door locks do not work from the inside, however I can unlock the door using the number pad. Interior lights, power seats and headlights all work. Battery voltage is 12.25V but drops to 11.89V when the headlights are on. Seems like a big coincidence to just happen to have the battery go bad while I was installing a wire. Are there any other things to check before I get a new battery?

 

That's a pretty healthy battery voltage drop for just having the headlights running. Have you tried jumping it with another vehicle or booster pack? My immediate thought is you didn't plug something back in at the fuse box... but with that voltage drop, it's within the realm of possibility that the battery is damaged (plate separation from a post, perhaps) thus causing the issue.

 

Did something else come loose around the battery power or ground cables? I agree that the voltage drop with just the lights on seems excessive. Battery terminals are clean and tight? Main ground (just in front of the washer reservoir) is clean and tight?

 

I suggest undoing what you have done.

 

You screwed something up. Check all the fuses. A (expensive) trip to the dealer may be in your future.

 

I tried jumping it. That didn't change anything. So I disconnected all the connections on the fuse box and reconnected all of them. That solved the problem. I'm not sure how any of the connections could not be totally connected since they lock into place, but something was definitely wrong. Problem solved.
I still have the issue of the voltage drop when the headlights turn on but the battery is the original. It might be on its way out.

 

I would suggest you fully charge the battery, then repeat the headlight on test to see what the voltage drop is then. A fully charged battery should read 12.75 to 13.2 volts. 12.25 volts is about a 60% charge on that battery.