boot/trunk remote closure

All working well thanks to both your help and instruction. Last thing I need help with if at all possible is changing the positive output pulse from pin 3 on the second 555 timer without using a relay.
I have tried researching using a transistor and resistors and have experimented on a breadboard but cannot get it to work. I even looked at NOT gates etc

The base of the NPN output transistor would be connected to the second 555 pin 3 through a 1k resistor, its emitter connected to ground, and the collector then provides the inverted output. If the ECU is happy with an open-collector output, then this is all that's required. If the ECU wants a pull-up to keep the voltage high when not activated, then put a (e.g. 1k ohm) resistor between the collector and 12V.