Recently bought a 2001 f150 4x4, noticed the horn not working, and found it was disconnected. low tone open so replaced it. Now it will not shut off. Have constant voltage to the coil side of the horn relay. disconnected horn switch at the clock s]ring connection under dash. still have problem. the keyless entry is not working, and the cruise control is nonfunctional. is my best guess that the bcm is messed up probable? Or is there another connection between these issues?

 

The 2001 doesn't have a BCM, it has a GEM. It's on the back of the under dash fuse box and is prone to moisture and corrosion from leaky windshields.

For the cruise control, there's an inline fuse in the recall harness to the disconnect switch on the master cylinder. The switch can leak and short out and cause fires, that's why the recall put a fused harness on it. Check the harness for continuity, if the fuse is blown and/or the switch is leaking, replace the switch and harness:


Keyless entry not working? Have you replaced the fob battery?

 

first thing i did. wasn't sure on modules, hoping gem was not involved lol should have known better. I'll check the cruise switch tomorrow thank you. still doesn't explain constant voltage to the horn relay coil, maybe just reset with battery connection. Trouble shooting 101 is it turned on? is mit plugged in? is the fuse blown? I remember that much in my dotage

 

Rock Auto calls it a BCM, but it's a GEM. They aren't that expensive (if your 4wd is electric shift) if you prove yours is bad:

https://www.rockauto.com/en/catalog/...ule+(bcm),2888

I dunno why the one for manual 4wd shift is 2.5 times more expensive.

 

thanks for clarifying that, 150 to 300 for gem is what I've seen.
I'll keep after it, gives me a puzzle to solve, and no rush as I have other vehicles, and am retired.

2.5 times more expensive because there are more sensors involved.

 

It's SUPPOSED to be there, that's how the relay gets power. The relay is switched on or off by applying a ground to the OTHER side of the coil.

Said ground is applied by either the switches in the steering wheel via the clockspring or by either the CSM (Central Security Module) or the RAP (Remote Antitheft Personality) Module, whichever is installed.

The GEM/BCM is not involved with the horn in any way. Do not spend money for one for this symptom.

 

Been too cold to work on it, still trying to determine which, and how many control modules are in this truck. thank you for the info, I thought there were two different modules involved, horn is security system, remote entry also. Cruise control is engine related so more likely involving main computer module, but think it is probably not the issue. More likely wire connection/ grounding issue.