I am making a trunk open detection alarm that will detect that the trunk of my car is opend by using a photocell to capture the light from the dome light of the trunk when it is opend.

How would I go about soldering a circuit that would somehow activate a switch that would complete the circuit from a 12v line, triggering the alarm when the photocell is sending voltage.

the green box is where i need assistance

 

Assuming this thread isn't closed,Why not just put a microswitch on the trunk body, so when the trunk is open it activates!

 

Why don't you tap into the truck dome light wire and be done with it ...
Also what if the bulbs burns out ??

 

There are better ways than to modify the car wiring, like a microswitch on the hinge or a mercury bulb or a rolling ball switch. Besides, modifying cars is not allowed at this site.

 

Maybe OP chose to do it this way because he/she knew the rules, and knew that the only way this discussion would be allowed to stay open is if there were no tampering with the car's electrical system; hence the detection of light - need not electrically interface with chassis wiring. Doubtful, I know, just playing devils advocate.

 

just get a mercury tilt switch and hook it to your dome light like you would any other switch...