Latched relay?

Oh wait....lol....now I get it....ok..your diagram shows rest at 12v+..... N/C for lock..N/O for unlock...wire it like this...Do we have a winner???

Did you look at the other Diagram?

Just use a 47uF Capacitor instead of a 470uF.

Are you sure that diagram will work?  Where is your voltage differential that charges the cap?  Looks like both sides of it will go to ground.

Yes this one works. The Transistor provides the voltage until saturation is achieved.

The capacitor charges at a RC time set by the components.

The capacitor starts charging when you short it out and release.

When the capacitor  gets to a full charge it turns off the second relay .

When in doubt, try it out !       When in doubt, try it out !

Where is the voltage supplied from that charges the cap?  From the top of the emitter back through the base?  Also, how is the cap discharging going to keep a PNP transistor biased? 

This is the Original circuit that I modified. Trust me it works.

OK, a little time with my 'scope and I see now.

I built the NPN version, using a 30K resistor, a 10K resistor, a 2n3904, and a 68uF electrolytic cap.

The two resistors in series form a voltage divider, making the base of the transistor more negative then the power supply.  When you short out the cap it discharges, and as the cap charges back up it allows voltage to pass through it.  Once the cap is full, it 'opens' and no more current flows.

I never would have thought to do it that way.

Hmmm... you know you are getting older when you don't have anything better to do at 2AM on a Friday night then learn how a new circuit works......