Sevel X290 wiring question: persistence of ign feed. (2016 pvc)

[Bertilak]

As a security feature, I'm intending to add a self-holding relay circuit to interrupt the fuel pump supply.
However it would be handy if I could connect the self-hold to a supply that stays on for a short while after the engine is stopped.
Does anyone know if there's an easy way to achieve this with existing system, perhaps coming off the timers that fade out the interior laps, or the radio is put back on?
Happy to do "electrics", but not really into re-coding ECUs...
Otherwise I'll have to add a timer module to re-arm the system, or do something else.

 

[pappajohn]

I think all you need is a normally open (N/O) automotive relay (when power applied the contacts close) so no need for a latching relay.
I would think the interior light fade would be powered from a capacitor after the ignition is off.
A relay may take more power than the capacitor can supply.

 

[Bertilak]

Thanks, I was thinking that the relay could be latched by a one-time press of a normal control function (say LH window up), after the ign is switched on. Switching off cancels the whole thing leaving the pump immobilised. Sort of like an ultra-simplified Van-bitz immobiliser, but at a few percent of the cost, suitable for an odd-ball diy pvc.
I thought a delay on cancel would be useful in case I stall it, or jump out for a few seconds, etc.