Last week I bought a used 99 F150 4.6l v8, it ran fine when i purchased it. It started up right away for the first week, then last night I went out to go for a drive and it would not turn on. When I would turn the ignition the battery light would come on. I got a jump and then everything was fine. Got home and went out about an hour later and the truck started fine. This morning went out and no luck same problem. It has gotten much colder here the last 2 days down to -20 celsius. Anyone know what the problem could be?

 

Maybe it needs a new battery?

Check the connections?

If the battery and connections check out ok it could be the megafusesor alternator....

 

I found this post
Well,

I have had a similar and still have that situation but found a workaround after fidling with key and even shifting in and out of park.

Up here (Ottawa Canada) it gets very cold and the colder the more this situation occurs. I suspect maybe it takes a while for the electricity to run through the system.

Workaround that seems to work well for me: Stick key in and turn it to start, you hear the click, take key out, put it back in and turn it to "accessory mode" and leave it there while you slowly count to ten, then turn it to start and off it goes.

Not a battery issue as when it cranks it does so with nice speed and on a new battery.

Hope this works for you...let me know

I went out and tried it worked perfectly. Any idea on how I could fix this, would a block heater work?

 

I just got threw working on a 1998 Ford F150 with the 4.2 V6 engine and I replaced the alternator with voltage regulator and put a brand new battery on it and the truck was still not charging. I also cbecked evry fuse as well. Well I had the alternator and battery checked and both came up good. Then someone said it could be the ignition switch under the dash so I replaced that also. Still no charge. Well I then started checking the 3 wire harnes on the alternator and only 1of the 3 wires was showing any voltage. SO I FIGURED OUT THAT THE GREEN WIRE WITH THE MAROON TRACER IS COMING FROM THE IGNITION SWITCH, WHEN YOU TURN THE KEY ON IT TELLS THE VOLTAGE REGULATOR TO START CHARGING. THAT WASN'T SENDING THE SIGNAL TO THE VR TO START CHARGING SO THE VR WAS SHOWING AS A BAD VOLTAGE REGULATOR (VR) . SO I RAN A WIRE OFF THE BATTERY STRAIGHT TO THE GREEN WIRE AS A TEMP FIX AND IT FIXED ALL MY CHARGE PROBLEMS.