This afternoon, I tried to start my truck after a couple of days of inactivity and it wouldn't start until I jumped it off. I then drove around for an hour or so and shut down, putting a battery tender on it.

Tonight I step into the garage and I hear some rapid clicking from underneath the hood. When I try to open the door so I can unlock the hood, it won't unlock using the power button. The courtesy light wouldn't come on either. Obviously the battery has run down again. I use the key to unlock the door, then pop the hood.

I track the clicking noise down to a relay which I believe is 46B (fog light relay). I pull the relay out and then put a regular charger on the battery.

I bought this 2007 truck in 2010 with 68k on it. The battery in there is a Motorcraft which I believe is probably the original battery. Externally it appears to be in excellent condition and the posts/connections are all clean. I recognize it's probably reached the end of its useful life.

I noticed some weird things: 1) with the truck on the charger and the fog lamp relay removed, the charger is drawing about 7-8 amps (after an hour or two). The door locks engage when I open the door. I then hit the door lock button and they disengage. I shut the door and they stay disengaged. I try to open the door again and the locks relock themselves. 2) I plugged the fog lamp relay back in and the fog lights come on. This is independent of the fog lamp switch position, which is off. The charger draw goes up quite a bit. The only way to turn the lamps off is to pull the relay. The charger draw drops back down to 7-8 amps.

Now I suppose it's possible the fog lamp relay got stuck on and that's what ran my battery down. But I didn't use the fog lights! The switch was off when I checked it.

I am OK with buying a battery as I'm sure I got my money's worth out of this one. But what else is going on? Should I just replace the fog lamp relay relay and see what happens? (While it initially was clicking rapidly when I first became aware of all of this, it no longer makes any noise when I plug it in; the fog lamps just turn on.)

What I am really trying to avoid is multiple trips to Autozone. I live on a barrier island and the closest auto parts place is 11 miles away on the mainland.

 

It gets weirder. The battery has apparently taken a full charge. Relay 46A and 46B are identical so I swapped them. The new(er) relay cuts the foglamps back on, even though the switch is off in the cabin. I pulled it.

I have discovered that while the pushbutton for the door locks will unlock all of the doors, only opening the doors will lock them. Or using the key fob... it (the fob) works as it always has... but the power button for the door locks won't lock them any more.

I fired up the engine and the alternator is putting out 14.2 volts according to my Scangauge. That looks normal.

This is just strange. It seems like the door locks and the fog lights have gotten confused as to what they're supposed to be doing.

 

Crazy electrical gremlins are almost always a short, and can be frustrating to find. You obviously already traced one fault to the fog light circuit, so just finish finding it and it may lead to your door lock fault. You shouldn't need a new battery unless you have repeatedly killed the old one, and hopefully you can just order parts online to save the voyage to the mainland. Good luck.

 

I took it in this morning to the dealer in Wilmington and got it fixed. Here is what they found: there is a "smart box" mounted over on the passenger side wall inside the cab that apparently got water in it and caused all of the gremlins. He dried it out and applied dielectric grease. Everything appears to be back to normal again. If the repair doesn't hold, at least we know where to start the next time.

My truck is normally garaged but I'd left it outside in the rain for the last three days while a northeaster blew through here. (It was hooked up to my boat and I just didn't feel like messing with it in the cold rain). The tech said it looked like the rain may have come from where my satellite antenna cable sneaks through.

I did not replace the battery because it appears to be holding its charge well. I expect it will eventually die but no point in buying one if it still has some life in it.

Thanks for the answer.

 

One time I had problems because I deep cycle charged a standard battery...