Hi my wife has a 1999 f150 5.4 my wife got out of work one day turned on the truck and it shut off. I headed over thinking all fudge fuel pump may have gone out, so eventually we got the truck towed and took a closer look. Iwas checking for disconnected wire or hoses of any kind everything was fine and dandy. Next checked the battery cables one terminal has a small crack , but while turning key their was enough power to give it some good cranks so eliminated that. Next I jumped in the driver seat tried to connect my obd scanner no power. I disconnected and tried obd on my other truck obd turned on went back to the f150 no power now I happened to look at the gauges again and theft was blinking fast while trying to turn on the truck. I checked both keys to see if I had a bad key both still didn't work reset the battery still didn't work. I set my key in forward position on for about 7-8 mins I notice the theft light wasn't blinking so fast then after several minutes I heard some clicking from the steering column so I tried turning the key truck turned right on been running the truck about 30 mins now and hasn't turned off. I turned the truck off and on about 20 times and no problems well for the obd connector now that's another problem now I'll check obd connection in a few days hopefully everything sets back into place. Hopefully the 7-8 minutes key in start posting works out for yall on the theft blinking light situation good luck

 

OBD2 connector is powered from the cig lighter fuse.

 

I know this is 8 years old, but I registered just to say...duuude. This was it. Replacing these two relays cured several ills, including motor shut downs, won't start/theft light, check engine light, odometer...

The key here that people need to be aware of is if any of these symptoms in addition to won't start/theft light are showing their ugly head, it's gotta be the relays. Not sure if you still look at this board midkid, but I registered just to say THANK YOU!