Okay so I just bought a 2002 F-150 5.4 to play around with and it ran perfect on the test drive. I stopped on the way home and when i went to get into the truck I started it and turned on the headlights. Pressed the brake (to put into reverse) and it dies and the odometer goes to dashes. I played around with it a little bit and I was able to press the brake with the lights off and it would stay running. Also I noticed when you press the brake pedal it turns on the headlights, just very dim. This is a very weird issue and I’m having trouble finding the right diagrams. Also if you are a Ford Tech and want to help me out, PM me and I’ll give you my number so I can explain better.

 

I have been learning a lot about these 97-03 ford 5.4l & 4.6l rigs the past 2 weeks or so.

My first thought is to check the: GEM (Generic Electronic Module). it is connected to the back of the fuse box located just above the emergency foot brake. They are known to develop Electrical Shorts "if the windshield has ever had a leak over that area".
If the GEM is bad, the fix is to find one in a junk yard vehicle and swap it out or purchase a new replacement GEM. Apparently all kinds of electrical problems (multipleat the same time) can arise with a faulty/shorting out GEM or use Box itself).

The GEM could be bad or... the fuse box is connected to it, could be bad.
The GEM is connected to the back of the fuse box.

*a GEM/Fuse Box handles these electrical circuits:
Warning chimes and warning lamps
One-touch down driver’s side window
Daytime Running Lamps
Heated rear window
Windshield washers and wipers
Battery saver
Remote keyless entry
Illuminated entry with remote keyless entry
Interior lighting
Perimeter anti-theft
Four-wheel drive

and possibly others. (I got this last piece of info off of another site not too long ago)

Watch this helpful YouTube vid about it...

 

Yes, check that, and also have your battery and alternator tested.

Local places like Advance Auto, Pepboys, AutoZone, O'Reilly's, etc can do it for free.

 

battery and alternator are good, just tested them. The GEM module does not control the headlamps or brake lamps so it’s not even in that circuit that I can tell. Also I cannot get it to act up again, I’m afraid to drive it around and have to tow it again.

 

Leave the GEM, battery, and alternator alone, there's nothing wrong with them.

You have a "bad" ground circuit.

Start by pulling the kick panels in the cabin and looking for body rot, corrosion or loose grounding connections.

 

okay will do! This truck does have some rust so I’ll start tracing down grounds. Today I removed the aftermarket alarm thinking that might be the issue, but it still did it. Electricity amazes me that a bad ground can cause head lamps to come on when pressing the brake or killing the engine .

 

That's because electricity always tries to find its return path to ground. When its intended path is not available, it tends to take detours through other paths with unintended consequences. Think of what happens when a plumbing drain is clogged...

 

here is my G201 ground. According to my diagram the brake circuit goes to this ground I’ve removed it and cleaned it, I guess we will see if it acts up again.

 

I would say that it looks like it needs a little help on the grounding there.

Here is one for you: A friend's truck would crank and then go dead.
We looked everywhere and found out that the fuse box fuse connection wire had backed out just enough to run and then quit. Bitch to get too to work on it as the fuse was good and just pushing on the fuse would keep it running. Never did blow the fuse, but the wiring harness under the dash at the fuse box was a bitch to work on.