Help us diagnose our Ford F150: what could be draining down the (new) battery overnight? We're suddenly seeing apparent battery drainage in our pickup truck, a 1994 Ford F150. Though the truck starts up fine, the dashboard battery gauge reads low immediately upon ignition, the windshield wipers are sluggish, and the dashboard lights are dim. We thought the old battery was likely dying, so we had it replaced with a new battery... but that hasn't solved the problem.
(I'm posting this for my husband, who drives the truck. Here is the problem in his words.)
It's a 1994 Ford F150 pickup. Two days ago, the battery light came on and the battery gauge on the dash was at the low end of the meter when I started the truck after work (it had been sitting for about 9 hours). I assumed it was a bad battery, so I had the battery replaced at a chain auto place.
Everything seemed fine until I got out of work that night (after the truck had been sitting for about 9 hours) and the problem was exactly the same. The alternator seems to be working, as the battery gauge goes up to where it belongs if I let the truck run for about 20 minutes. There are no lights left on (glovebox, dome light, etc). It seems that, when the truck is off, something is drawing power from the battery.
When the gauge is low, the dash lights dim, and the windshield wipers are slow and sluggish. When it's charged back up, everything is normal again.
While I'm letting the truck idle to charge up the battery, the gauge will go up slightly if I rev the engine, but goes back down when I take my foot off the gas. Once it's fully charged again, revving the engine has no effect.
Both before and after getting the battery replaced, the truck started up just fine (no problem at all), even though the battery light came on and the battery gauge was low.
Once the battery is charged up again, turning the truck off for ten minutes-a half hour has no effect; the battery is still charged normally after that length of time.
We'll be taking it in to the mechanic on Monday, but with holiday errands and visits pressing, we'd love to get a headstart on the diagnostics over the weekend.
Some specific questions
1. Aside from the things we've checked (dome light, glovebox light, ashtray light, radio), what could be draining down the battery while the truck is off? Especially, do you know of any idiosyncratic drainage problems with the Ford F150? (We're also checking the forums on a Ford-specific board, but any hints would be helpful.)
2. Are there any simple home diagnostic tests we could make? Again, anything specific to the Ford F150 would be useful, but not necessary.
The fact that the truck starts normally
(that is, readily and vigorously) seems to make this a different question than previous AskMe questions (which all seem to include a car that won't turn over) about a drained battery or dying alternator... or am I wrong? If the alternator is faulty, would the car be starting normally?