it can also be...
Bad cables. Seen lots of bad cables recently. Some corroded at the battery post itself. Some inside the insulation but up near the battery connector. You can't see it, but the copper wire has been corroded into mostly green/white powder that won't conduct. Ditto for ground cable.
The easiest way to test this is to take a good set of jumper cables, and connect the black to the - battery post, and the other black end clamped against a good ground like the alternator bracket. If things work, the ground cable is bad. If not, connect the + end to the + battery post, and the other + end to the + connector on the power distribution panel (just trace the red wires from the battery, one goes down to the starter, the other goes to the power distribution box. If things work now, the + cable is bad. If not, then the problem isn't either of those cables and you keep tracing to see where +12 drops to zero, probably behind a fuse or with a missing ground elsewhere.
Bad cables. Seen lots of bad cables recently. Some corroded at the battery post itself. Some inside the insulation but up near the battery connector. You can't see it, but the copper wire has been corroded into mostly green/white powder that won't conduct. Ditto for ground cable.
The easiest way to test this is to take a good set of jumper cables, and connect the black to the - battery post, and the other black end clamped against a good ground like the alternator bracket. If things work, the ground cable is bad. If not, connect the + end to the + battery post, and the other + end to the + connector on the power distribution panel (just trace the red wires from the battery, one goes down to the starter, the other goes to the power distribution box. If things work now, the + cable is bad. If not, then the problem isn't either of those cables and you keep tracing to see where +12 drops to zero, probably behind a fuse or with a missing ground elsewhere.
My dads 00 stang did the same thing. Door locks worked, dome light worked, car drove perfect to and from town. Shut it down for like an hour and went to move it to its normal parking spot and "click click click". the door chime sounded a little funny, and even the headlighst worked (but not well)...just didnt have enough juice to turn over. Apparently a few cells shorted out....I think the green was still showing on his battery as well.