Battery keeps draining, 98 wont fire up if sititng overnight

[TeamPwnageBrad]

Hello, Ive got a 98 4.0L SOHC XLT Explorer and for some reason it keeps killing batteries. The alternator is a brand new high output alternator (250A @ 2000RPM) and has been working absolutely fine for the past month. The battery is about a 6 month old Optima D31 deep cycle battery. It also tests out fine under a heavy load.

I drove from austin to houston and parked it and everything was fine. the next morning i came out and i saw that on my head unit the voltage was reading ~12.8 to 13v at maximum, even whiile driving around at 2k+ RPM. Sounds like an alternator problem there... get home again and park it. come out the next morning and the thing wont turn over. the battery voltage was at 9.1 volts so i removed the optima and stuck it on the charger. I threw in my backup battery and the car fired right up. the head unit was showing 13.4-13.5 volts. it usually reads about .3 lower than if you were to measure at the battery terminals. So i figure its charging fine right now, its just a little low because that battery has been sitting and is taking a bit of current and charging up. I turn the car off, the battery is sitting at 12.5 volts. I come out about an hour later and it fires up. This morning, i came outside and it wont start. 9.1 volts again. And now we are at the present.. Im thinking that there is a relay stuck somewhere that isnt turning off and is sucking up a decent amount of current.

If anyones got any suggestions, im open to trying them all.

 

[budwich]

Start looking at your power option stuff and checking to see stuff that should be off when there is no key. Check to see if all your lights are off... dash, courtesy, dome. Perhaps a long shot... but maybe even the "infamous ford fire" brake pressure relay partially shorting.... on its way to a fire!.... :-( The other method is unplugging either options or fuses to stuff that you don't need and see if that helps.

 

[TeamPwnageBrad]

ive checked the lights inside. they all appear to be off, but with only 9.1 volts (probably less now) they could be dim enough to where i cant see em in the daytime. What is the infamous ford fire? i havent heard of this. Sounds like something i need to check out.

Thanks for the response

 

[TeamPwnageBrad]

maybe i shoulda put this in 911

 

[budwich]

if you do a search on "Ford Fire", you should find a lot of threads both inside here and on the internet. Basically, the brake pressure switch fails because of a leak (to brake fluid)... in some cases, a fire can start. In others (there was a thread here recently) where a fuse was blowing continuously and ultimately the owner was pointed to the pressure switch and just in time as it started smoking shortly there after. Anyways, its just a thought... probably not in the right direction but it does have power on it all the time.