So I have a 2000 F150, 4x2 Automatic with the 5.4 in it. I have this electrical issue that is driving me crazy. So the vehicle will jump start, runs about a 1/4 mile and then the battery gauge drops to nothing and it dies. Theft light is blinking, battery saver relay is clicking away loudly, dome light is flashing and sometimes there is a clicking sound also from under the hood. I have currently pulled the fuse box and GEM module and everything looks clean and corrosion free. The guy I bought it from says it had a new starter and new alternator installed months ago. Also from time to time the starter doesn't engage the flywheel. Any ideas?

 

Sure sounds like a **** up alternator to me

 

New alternator in it and battery problem has calmed down some. Issue is now when I hit the window switch the voltage drops off like a rock. Also the odometer doesn't show up, theft light is back to normal, battery light stays on, radio works fine.

 

Low batteries are notorious for making vehicles go hay wire... are you sure your battery is good and strong? Have you had it tested? How old is it?

Side note have you notice this happens after rain?

 

8/16 is the date on the battery. A little old but eh, oddly enough hitting 3 grand to 3,200 the damn battery light goes off. I live in the desert. So no it isn't something that is happening after any rain.

 

Battery light indicates something is wrong with the alternator or it's connections, not the battery. It's a charging system issue. These trucks seem to not like aftermarket alternators for whatever reason.

 

Yeah if higher rpms sends the battery light off (which yeah it really should be call an alt light) then I'd be looking at your alternator. The box store alternators are usually junk. It sounds like the PO already dumped the original. If you have the time I'd hit up a junkyard for one, run it till it dies and then have it rebuilt (or rebuild it before putting it back on if you have the downtime availability)

 

I have that sneaking suspicion that I took the original symptoms I got and went too far with my troubleshooting and need to quit overthinking and go back to basics and check the easy stuff first. I bet I am missing something so simple in a basic charging system.

 

Have you put a DMM to the system? That will quickly tell you if your alt is working or not. Always start with the simple things

 

The battery saver function shouldn't be working with the key in the ignition. It's a GEM function that has a timer to turn off lights or anything else connected to it when left on. How it works depends on if you have remotes or not. My opinion is your GEM module has a problem with wiring since it requires a jump to start. Then again, low batteries can cause unusual problems also.