1999 Mercedes-Benz E320 Trunk Won't Open Despite New Actuator

Most likely cause here is a wiring or connector issue feeding the trunk actuator. Since you replaced the actuator and it didn't fix the problem, the actuator itself is probably not the root cause. The wiring harness or connectors often get brittle, corroded, or broken over time, especially on a 1999 with 215k miles.

Most likely culprits

• Wiring harness or connector to trunk actuator: Common failure point, especially with age and exposure.
• Trunk lock switch or release button: If the signal never reaches the actuator, it won't open.
• Mechanical lock cylinder: If the key won't turn or release mechanically, linkage or cylinder could be seized.

How to narrow it down

1. Check for voltage at the actuator connector while pressing the trunk release button or using the remote. If no voltage, wiring or switch is suspect.
2. Inspect wiring harness and connectors for corrosion, broken wires, or loose pins. Wiggle wires while testing voltage to see if intermittent.
3. Try manually unlocking the trunk with the key in the lock cylinder. If it doesn't turn or feels stuck, mechanical lock cylinder or linkage may be seized.
4. Test the trunk release switch/button inside the car. If no signal output, switch could be faulty.
5. If wiring and switches check out, scan for any central locking module faults. Less common but possible.

Possible parts (if needed)

• Wiring harness or connector repair kit for trunk actuator
• Trunk lock switch or release button
• Trunk lock cylinder (if mechanical operation fails)

A few questions

• Does the trunk lock cylinder still turn and mechanically unlock the trunk?
• Does the trunk release button inside the car or remote unlock other doors normally?
• Have you checked for voltage at the actuator connector when trying to open the trunk?