I have a 1994 f150 4x4 4.9L. I have problem with my batery it drains during the night . at first I thought it was a bad batery and I bought a new one, same problem I had the alternator tested and it is good. All I can guess is that somthing is staying on when I shut the truck off or maybe somthing is rong with the swich. I appreciate any help if anyone has an idea

 

Try pulling a different selection of fuses from the panel each night and see if you can narrow it down to a particular circuit

Also your new battery will be toast quickly if it goes flat every night. You can buy inexpensive Digital volt meters (wallyworld) and measure battery voltage whilst pulling the fuses and waiting halfanhour or so

 

It most probably deals with circuit that works with key off. I'd check for a glove compartment light that does not go off when closed or similar. I doubt that it would draw enough amps though. Do you have any hot wired accessories like trailer brake booster, aux. lights, refrigerated toolbox, diesel transfer fuel tank pump, amp, cb? Some radios have been installed/wired wrong to stay on with key off. Voltage regulator in the alternator could possibly be "on" but shouldn't with key off. Another possibility could be in the ignition switch. Do you have teenage kids/neighbors who like music? Doubt you leave the key in though. I live in a very rural area. Something that can be on with key off, like a light circuit or cigarette lighter can draw amperage if the hot wire grounds out (doesn't always blow a fuse and sometimes fuses have been replaced with one larger than specified for a circuit), insulation is rubbed off and shorts to frame/ground. I frequently notice shorts on farm/logging equip when I pull battery cables for cleaning and they spark going back on. Most of mine have battery disconnect switches so there is no ground with the switch off unless there is a short. May not work on a EFI truck if pcm has some continuous current for memory (also radio clock draws very little amps). Some 4.9L have a electrical cooling fan on passenger side of engine bay that runs after the truck is killed, does yours? I had one on F250LD '89 model 4.9L 4x4. Maybe some other electrical demon/symptom will show up. I hope not but good luck. The fuse pulling advice will really help to isolate the circuit. Don't forget those under the hood in the power distribution box near air filter though. They run pcm, fuel pumps, trailer tow, etc. You can also verify if all lights work and other electrical circuits. If you can find another fault, it can be helpful. Have you replaced anything lately electrical or even phsical that have pinched a wire, like a fuel tank ?

 

A while back I had a problem with my battery draining at night or during the day while parked on the jobsite. Turned out my fuel pump relay was toast, causing my high pressure fuel pump to run even after the truck was shut off. Sure didn't take it long to kill the battery. I was stumped untill I bought a new battery, hooked it up and could barely hear a buzzing sound coming from the pump. Someone from this sight told me to smack the relay box to shut it down, which I did for a few days untill I was able to replace the relay.

Dont know that's your prob or not, just wanted to throw my two cents in....

 

http://www.inliners.org/tech/tech6.html

This should help.

 

I had problems with my fuel pump relay. Wouldn't do it all the time, so it had me going. Finally happened to hear the pump running one day while the truck was shut off. If that's the problem you can hear it running, the Ford pickup pumps seem to be quiet, so you have to get close to hear it.

 

draining battery.
Might be a bad ground.
That will cause it to drain.

 

Not sure how a bad ground could drain battery. A bad or good ground should be irrelevant with key off. I would put a DVM on the wires at your ignition switch and see where the power is staying on.

 

All power voltage wires from battery do not go through the ignition switch. Some circuits such as lights, cigarette lighter, and I'm sure others that are more essential will come on regardless of where key is positioned or even if key is out. Voltage loss in these circuits won't show up by testing at the ignition switch but since others might be, it is worth a try. If battery drains overnight with key off I doubt the bad circuit will go through the ignition switch though.

 

That's a good point Tim, but the ignition switch is the first mechanical interface with the power supply. It's a place to start anyway.

 

I had the exact same problem. Bought a new battery and it did nothing to cure this. Had the alternator tested and was told it was good. However, the diode pattern was burned in the alternator. Installed a new alternator and the problem was gone. Hope this helps.

 

replace the "VOLTAGE REGULATOR" .

 

I mentioned that 4 days ago. I'm sure ther is a way to test it with the alternator still on the truck. Regulator should turn off with the key but main voltage wire will still be hot. I can't say which wire to check right now. Most of my logging equipment has Cummins with the Delco alt. I just replace the whole alt. on my trucks. It is common on the Delco for the regulator to go out but normally it just won't charge. We run the wire through an oil pressure switch also so no "charge" with engine dead which would drain the battery just like leaving the key on. I believe Ford will be similar but not exact since they started using the internal regulator.