I fixed my 300M's center brake light, but ...

My center brake light quit, and I discovered that there was no
continuity between the connector on the inside left side of the trunk
(behind a lining) and the connector adjacent to the bulb socket, so I
bridged it with heavier-gauge wire (12ga). The light works again, but I
find that the alarm sometimes goes off when I open or close (no matter
how gently) the trunk.

Any ideas what is happening here? Could using a different gauge wire
(the original was probably 16ga or maybe 18ga) upset the system's
equilibrium? What is it that the alarm system is sensing?

Perce

"Percival P. Cassidy" wrote:

> but I find that the alarm sometimes goes off when I open or close
> (no matter how gently) the trunk.

Is the car in locked mode (alarm-armed) when you open and close the
trunk and the alarm goes off?

Or is the car in unlocked mode - and the alarm goes off when you use the
key-fob (or the dashboard-mounted button) to open the trunk?

"Percival P. Cassidy" wrote:

> I find that the alarm sometimes goes off when I open or close (no
> matter how gently) the trunk.

Here's your problem:

With the VTSS (Vehicle Theft Security System) ARMED, opening the trunk
(Deck Lid) triggers an alarm.

The deck lid has a Knock Out Switch that lets the BCM (Body control
module) know if the lock cylinder is either in-place or has been knocked
out.

If the cylinder has been ‘knocked out’ or (as I believe in your case)
the wiring to the switch has been damaged, when the lid is opened and
the Deck Lid Release Solenoid/Ajar Switch sends it’s ‘Ajar’ signal to
the BCM the VTSS will trigger the alarm.

I would guess that you have a wire break in the deck lid’s wiring
harness.

There are several wires in that harness (release solenoid, high mounted
stop lamps, grounds, etc.) and I suspect that you have a problem with
the power feed to the ‘knock out’ switch.

Check the harness where it transitions from the ‘deck lid’ proper to the
interior of the trunk. That’s where you'll find any wire breaks. The
harness flexes a lot there and over time something can give.