I have a similar problem with my 98 F150, (5.4 xlt, 60k miles) but not exactly the same as described. Occasionally, maybe 4 or 5 times a week, my door ajar light and my cargo light will stay on, but the dome light goes out as normal. Also, the automatic door locks won't activate when it does this. It may go out in 2 blocks or it has taken 30 minutes on occasion. Once the light goes out the door locks work with the next brake application. This has been happening for about 2 years now, but is getting worse. But wait! There's more! Sometimes when I turn off the truck and walk away the cargo light and door ajar light stay on for maybe 20-30 minutres, but the dome light goes out normally. Also, seemingly unrelated, the wiper speeds go erratic with increasing regularity.

I was told by a cause & origin investigator for a major insurance company that a lot of fires are occurring in F150s and Expeditions with the 5.4, at approx 70k miles, and it's caused by the "speed control." (His words) He said that he has examined hundreds of these controls and there is darkening from heat spreading across the circuit board directly relating to the mileage.

I am under the impression that the GEM controls all the functions mentioned above, including the speed control. Could all this be related?

 

Hi pcollins8872 and welcome to FTE

It certainly seems like you might have a GEM problem. Yes everything ties in to there except the speed control. I've never heard of a speed control fire.
I would check for a windshield leak. Quite often the windshield will leak and water will drip into the GEM and fuse box causing all sorts of problems. It doesnt take much water to make a mess of it. Uusally you can see stains above the GEM if there has been any water leaking there....looks like trails in the dust.
Let us know what you find.

 

I've had the dash opened up recently, once to install a new stereo and to install a new instrument panel face. Nothing like that noted. Also, it does this noticeably more when the day warms up and the truck is parked in the sun. It does this when it hasn't rained for weeks too. Where exactly is the GEM? I'll have a look. Thanks.

 

The GEM bolts to the back of the fuse box. You have to remove the lower dash trim and then the fuse box. It's a bit of a pain getting the wiring connectors off the fuse box and GEM, especially the first time.