I've been dealing with a strange power lock issue for a while now. The vehicle is a 2002 F250, 7.3 diesel (crew cab, lariat) with an aftermarket Audiovox/Prestige (APS-786) alarm & remote starter. Occasionally, especially it seems, when it is hot or the truck has been driven a lot to make it hot, the function of the lock and unlock buttons on the truck reverses! Pushing lock (on the front door panels) - unlocks the doors. Pushing unlock - locks all of the doors. The behavior is even more frustrating when you use the wireless alarm key fob. Pushing lock - unlocks the doors and arms the alarm. Pushing unlock - disarms the alarm but locks all of the doors!

The alarm came installed in the truck when I bought it. I recently took it all apart and reverse engineered the alarm install. Everything appears to be installed correctly and works correctly some of the time.

The truck was recently in the "confused" state and I checked the wiring in the truck. Providing a ground pulse to the lock wire (white w/ red stripe) in the door panel unlocked the doors. Similarly, providing a ground pulse directly to the unlock wire (black with white stripe) locked all of the doors.

It appears that somehow, the logic gets reversed by the truck. Has anyone ever heard of this? Is this something that the factory security module could be causing? Anyone have any ideas on how to fix or troubleshoot this?

 

The security module would be a good suspect. It's under the dash, mounted sort of over the hump in the floor.

 

Me thinks a bad alternator would cause it too......

 

How would a bad alternator lead to this problem? I'm not ruling it out, I'm just interested to hear why you think that this could cause the issue.

Where do I begin with the factory security module? I have the wiring diagram, but don't really know where to start. It seems like the relevant diagrams are on pages 59-1, 59-2, and 117-3 of the Wiring Diagrams book.

 

Well, the security module is the brain behind the door lock functions. You might also check all TSB's related to your truck, and go talk to the service department at your local Ford dealer and see what they say. Someone may have some insight or have run across this before. My Local Ford dealer is friendly to me when I go in and ask questions, though that may be the exception instead of the rule.

If you can get the truck hot and make it fail, you might want to get some cold spray and spray it on the security module, and see if it clears up.

 

I'm sorry you're having this isue, but LOL!!! this is the funniest thing i've read in weeks!...

I just imagine the situation and i can't help but laugh... Anyway, check the wiring, i bet some wire got caught where it shouldn't and it's receiving a lot of heat. If there is any sort of module that controls the locks, i would search for the same. It does sound like it's heat-related.

 

I admit that it is a pretty funny problem. Had me scratching my head as to what to do the first couple of times it happened.

I dug up another piece to the puzzle today. I have my original Ford factory key fobs. I got the truck into the confused state with the aftermarket alarm fob. The door lock/unlock button functions is reversed as I originally described - BUT, the factory fob works just fine. After successfully locking and unlocking with the factory fob, the door buttons and aftermarket alarm remain mixed up.

It makes me think that the alarm is wired incorrectly. Its as if the alarm is triggering the lock/unlock downstream from the VSM without letting the brain know whats going on. This then leads to the confused buttons somehow?

 

If the alternator puts out an A/C voltage (which it can do if a diode is bad or has an intermittent connection) it can cause all kinds of different screwy things..... One I had did it to me by turning on CEL for a bad secondary air pump. Air pump was perfectly ok.....Alternator tested good!

 

Make sure to research how the aftermarket alarm is wired. In the older Fords, they were always special and required add-on relays because Ford used a little motor for their door locks, which works just like the electric windows. The Ford door lock switch was wired to switch the polarity to the door lock motor, which made it lock or unlock. Most aftermarket alarms just gave a pulse to lock the doors, which was not good enough for the Fords, and relays always had to be added when puttinq a aftermarket system in a Ford.
But you have the later model, which only needs a ground pulse to the security module to make them lock or unlock correct? So that rules all that out, unless someone has wired it wrong.

After saying all that, I believe I would disconnect the aftermarket alarm completely, and make sure to check for any damage they may have done to the wiring. That has happened before on here, the installer had damaged some of the wiring harness while wiring the alarm in place.

 

That was kind of my thinking too. I did some of that recently. I pulled everything out, traced and labeled all of the wires, and walked through the install manual to see that everything made sense. I cleaned up a couple of spotty looking splices and relocated the ground location. Still had the same problems though.

There are a couple of features that weren't setup with the original install though that I'll probably try to sort out: dome light relay and 2-step locks. I'm hoping that in the process of setting up the 2-step locks I'll uncover something. I'm planning on relocating my lock/unlock splices to closer to the VSM instead of in the driver's door jam. Right now, most of the alarm wiring is just jammed up behind the fuse box and isn't very clean.

Still, I'm trying to figure out what kind of failure mechanism would cause the hard-wired door switches to get reversed. That one still has me stumped.

 

Resurrecting an old thread here.

I was looking at the wiring diagrams for my truck (2002 F250 PSD). The Door Locking connector (C2113a) from the Vehicle Security Module (VSM) has Door Lock/Unlock output connectors and also Door Lock/Unlock logic connectors. The remote control alarm and locks section in the wiring manual (pages 117-2 and 117-3) shows the logic wiring, but I'm having a hard time figuring out exactly how it works. Does anyone know how the door lock/unlock logic connectors work? It seems like the interplay between the logic and output connections may be causing some of my problems.