Delayed release relay circuit help

There's a wire that signals the engine is running?

Because you have several conditions i think a micro controller is going to be the answer...

 

How do you know the voltage reverses??

 

You should consider Harald's suggestion of that timer or something similar.
A slight modification will allow you to use the 'door unlock' signal to turn the device on. Using a relay, and a couple diodes will allow you to use the 'door lock' signal and any other signal to trigger an additional relay or transistor to reset or turn off the device.

Your call though...
Additionally, you could experiment with a micro-controller which would most likely cut down on the size of the module and allow you to fine tune it exactly as you want it to behave.

First steps will always be:
-Identify what you want to monitor.
-Identify the wires that carry the signals or voltages that directly relate with what you want to monitor.
-Identify what the wire carries. (signal, active ground, or power)
-Design or find a system based on the above requirements.

Haynes manual or service manual is incredibly helpful here.


And @Colin Mitchell , It's INCREDIBLY common for the electric locks in a vehicle to be operated with a Relay-based H-Bridge that is controlled by two signal wires. The signal wires don't change polarity, but the power to the actuator does. Which wire will be tapped into will be up to the op.