07 Town Car LCM buzzing help

[Scooters Garage]

Looking for some help. The Light Control Module on 07 Town Car started buzzing intermittently about 6 weeks ago. It’s currently not causing any critical issues but I’m trying to get it taken care of before it does become critical. We’ve owned it for about 8 months. I’ve done the following troubleshooting and repair attempts so far without change. This is initiated by either unlocking remotely or by key.
LCM module number 7W1T-13C788-AA
1. I inspected and cleaned the A and B pillar, front driver and passenger fender body grounds.
2. Inspected splice by A and B pillar.
2. Pulled and replaced all relays in LCM myself.
3. New battery.
4. Disconnected drivers side head lamp connector while buzzing. No change.
5. Replaced the headlight multifunction switch.
6. If I pull either passenger compartment fuse F23 or F26 buzzing stops.
7. Buzzing stops after it warms up for a little while. Sometimes 30 seconds sometimes a couple minutes.
8. Lights and side markers flicker when buzzing as long as headlight switch is in off position. If I turn headlight switch into any other position the buzzing stops. Nothing stays on that after buzzing stops that I’m aware of.

According to the 08 factory manual F23 goes to something called “Logic Batt” F26 goes to “Batt2” in the LCM. Manual doesn’t explain what those are. I have the manual for the 08, not the 07. I’m hoping they are the same. Short story is I ordered the 08 manual thinking I was buying a 08. Surprise when title came in as 07. Anyway.

Any insight into what might be causing this would be helpful. I’m at the point where I’m going to buy back probes to start checking at the plugs. I’m also beginning to suspect that something is telling it to do that.

 

[Scooters Garage]

Ok. I’ve sat down and reviewed the electrical schematics and am wondering if the issue is with the Light Sensor. The part number appears to be 13A018. However for the 07 it looks to be an updated part number “unobtainium”. Local pull a part looks to have 2 08 Town Cars on lot. I’ll go see if I can get one or two tomorrow. If not I’m probably going to try to unpin the wire from LCM and see what happens.

Anyone ever had this. I’ll report back.

 

[driller]

I've looked into this as I recall hearing this being an issue in the past.

Apparently other Town Car owners have heard such buzzing which could be tracked to the LCM. The predominant theory is there is a relay in the LCM that is doing the buzzing. Relays have a propensity to do this if there is insufficient or unstable voltage to the relay. This could be the relay itself, a poor connection internal of the LCM or some cause of insufficient or unstable voltage outside the LCM.

I would advise to check and monitor the voltage input(s) to the LCM when it is buzzing and compare them to when it is not buzzing. A methodical process of elimination may reveal the source of the problem.