97 Town Car Alarm Won't Stop Going Off

[Joe Dudebro]

Let me preface this post by stating that, before anyone asks, I have gone through the electrical schematics; I've deactivated all sensors to the alarm system; I've changed key fob batteries; I've changed the car battery; I've disconnected the radio; and yet, the problem persists.

The only thing I see left on the schematic is the input for the alarm condition on the ECM. With none of the sensors connected, it shouldn't even *receive* a signal yet somehow, the car just keeps randomly sounding the alarm. It may go three months without going off, and then, it won't go three minutes.

I'm at my wit's end with the thing. It's my grandpa's old car, and it's relatively low miles and was garage kept, so it's *nice*. It just keeps sounding the darn alarm. As a temporary solution, I've installed a remote battery disconnect relay on a keyfob, so I just disconnect the battery every time I shut the car off. I don't like this solution, however, because it's hard on the battery, and (minor annoyance) it won't remember the last- used radio station/AC setting/time.

Does anyone have a suggestion on this? My grandpa said he'd taken it to Ford a few times, and they couldn't figure it out. I'm just curious if anyone else has had this specific issue. Honestly, it's feeling like an ECM glitch at this point, and I really don't want to go that route.

 

[Action]

Welcome to the LOG!

I do not have your solution.
One of the things you did not state was the check engine light is not on, and I assume there are no codes.
If correct, this means the ECM is good and the issue is external to the ECM.

If you have not invested in a factory shop manual, I would do so. There would be an extensive diagnostic section in this manual.
The sensors are really easy to check. I believe they are normally open. use an ohm meter to verify operation and reinstall correctly and properly adjusted.

Your assumption about the ECM not receiving a signal has a flaw. The does not include a crimped wiring harness or a bad/dirty connector.

Good luck.


Action

 

[Joe Dudebro]

Welcome to the LOG!

I do not have your solution.
One of the things you did not state was the check engine light is not on, and I assume there are no codes.
If correct, this means the ECM is good and the issue is external to the ECM.

If you have not invested in a factory shop manual, I would do so. There would be an extensive diagnostic section in this manual.
The sensors are really easy to check. I believe they are normally open. use an ohm meter to verify operation and reinstall correctly and properly adjusted.

Your assumption about the ECM not receiving a signal has a flaw. The does not include a crimped wiring harness or a bad/dirty connector.

Good luck.


Action

Correct, there's no check engine light, battery voltage is fine, and I have comprehensive wiring schematics for the thing. A dirty connector or bad crimp... eh... maybe? The issue is that, with the sensors all deactivated, none of those alarm states should set regardless.

Now, if the ECM has a bad connection, that could possibly do it. Could be that it's detecting low voltage (something I've discovered causes nuisance trips on these) and thus setting the alarm off. I'll take a look at it this afternoon.

 

[wa9zug]

Hmm https://charm.li/Lincoln/1997/Town ...ctrical Diagrams/Antitheft and Alarm Systems/

Maybe ignition cylinder tamper switch?

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[etinpa]

I don't have a solution but I'll run down what I see on the schematic in case a second set of eyes turns out to be useful.

First, I don't see the alarm connection to the ECM. Which pin does that connect to on the LCM so I can look further?

I see the following connections that, when grounded, indicate an alarm condition:
Trunk Lid Anti-Theft Switch
Anti-Theft Hood Switch
LF Door Ajar Switch
LR, RR, RF Door Ajar Switches

There's a connection from the LF Door Module for Panic but I'm not sure if that is active high or low.

There's a two wire connection to the Ignition Cylinder Tamper Switch that appears to be closed in the normal condition (open circuit to alarm).

Let me know your thoughts on the above...

 

[Wayne A. Pflughaupt]

When I had that problem on my 2003 model, it was a bad door ajar sensor intermittently making and breaking contact. Tough to figure out which in your situation, but the first go-to would be to replace the one for the driver's door.

Regards,
Wayne A. Pflughaupt

My 2003 Cartier

 

[Joe Dudebro]

I don't have a solution but I'll run down what I see on the schematic in case a second set of eyes turns out to be useful.

First, I don't see the alarm connection to the ECM. Which pin does that connect to on the LCM so I can look further?

I see the following connections that, when grounded, indicate an alarm condition:
Trunk Lid Anti-Theft Switch
Anti-Theft Hood Switch
LF Door Ajar Switch
LR, RR, RF Door Ajar Switches

There's a connection from the LF Door Module for Panic but I'm not sure if that is active high or low.

There's a two wire connection to the Ignition Cylinder Tamper Switch that appears to be closed in the normal condition (open circuit to alarm).

Let me know your thoughts on the above...

Curious... somehow I missed the ignition tamper switch. I'll have to see if I can take a look at it. I know that grandpa did have to get the front end of the car rebuilt after he hit a concrete barrier once, so it's entirely possible that something has either come loose, or was damaged during re-work. There was extensive damage done to the dash, so I wonder if that tamper switch isn't the culprit.

I'll have to report on my findings Tuesday. Tomorrow is a long day for me.

Thanks for the suggestions!

 

[oktowncar]

I don't have a solution but I'll run down what I see on the schematic in case a second set of eyes turns out to be useful.

First, I don't see the alarm connection to the ECM. Which pin does that connect to on the LCM so I can look further?

I see the following connections that, when grounded, indicate an alarm condition:
Trunk Lid Anti-Theft Switch
Anti-Theft Hood Switch
LF Door Ajar Switch
LR, RR, RF Door Ajar Switches

There's a connection from the LF Door Module for Panic but I'm not sure if that is active high or low.

There's a two wire connection to the Ignition Cylinder Tamper Switch that appears to be closed in the normal condition (open circuit to alarm).

Let me know your thoughts on the above...

I agree with etinpa.
Switches are physical movement items and thus prone to wear, corrosion when exposed to the elements.
I would focus on those, clean and lubricate the switches with a fluid film product to help protect things and go through the rest he listed

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[ogre01]

An excellent product for electronics cleaning is DeOxit Gold. I've used it on my steering wheel controls with great success (have used it for years on antique radio boards). Plastic safe (non-harmful solvents), cleans well, and it does protect with a non-conductive film. I'd spray in switches, while operating, and see if that works prior to any disassembly.

 

[Joe Dudebro]

When I had that problem on my 2003 model, it was a bad door ajar sensor intermittently making and breaking contact. Tough to figure out which in your situation, but the first go-to would be to replace the one for the front door.

Regards,
Wayne A. Pflughaupt

My 2003 Cartier

Yeah, I flat disconnected that one just to see if it made a difference. It did not. As we speak, the trunk release/soft close mech, hood Switch, and driver's door switches are disconnected. I'm pretty sure I disconnected all the sensors for the other doors, but it's been a little while since I messed with it. I'll have to do a little detective work.

An excellent product for electronics cleaning is DeOxit Gold. I've used it on my steering wheel controls with great success (have used it for years on antique radio boards). Plastic safe (non-harmful solvents), cleans well, and it does protect with a non-conductive film. I'd spray in switches, while operating, and see if that works prior to any disassembly.

Huh, never heard of that one. I'll give it a look-see. Thanks!