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2005 F150 middle of the night horn blowing and mystery fire

  • heyinway
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21 Nov 2019 14:03 #35182 by heyinway
I've heard of this happening, but not experienced it.

First things I replaced when I bought it was battery, alternator, serpentine belt setup, tires, struts, and shocks. Battery and tires were only things not originally on truck when built.

I was having issue of it draining battery after couple of days. Battery tested good. Truck sits unused most of the time so I cut to the chase and installed a disconnect switch. I've since "retired" and have time to tinker with it.

Electrically the only other change has been the fuel pump control module. Found its' case to be split open from corrosion when I took spare tire out of under bed holder. Circuit board completely exposed, I couldn't believe it was functioning. Wasn't have any fueling issues. Replaced it with the updated "stand-off" style.

Wondering if that module stays awake for a while after key off ?

Or something in the system not going to "sleep" that is common to that era truck ?

Its a Pittsburgh area rust belt truck.

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  • Tyler
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23 Nov 2019 10:16 #35233 by Tyler
That generation of F-150 has a few different sources of battery drain. :( Alternators are one, even replacement ones. The easiest way to spot one is to let it sit overnight and check the alternators temperature in the AM with an infrared thermometer. It shouldn't be warm.

Second is the door latch switches. They can either fail to close entirely, or open up on their own later on while the vehicle sits. That may account for the horn going off in the middle of the night.

The GEM modules themselves have also been known to keep relays energized when they shouldn't. It's more likely on vehicles with water intrusion.

I've never known an FPDM to cause a drain, but anything is possible. :silly:

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