Hi polaris,
I feel sure we can help to do exactly what you need.
I get the impression that electrics is unfamiliar territory to you.
Lets start with some simple semantics.
When the relay coil is operated, lets call that 'engaged'
I am going to assume that you are referring to the relay's coil.
I am also going to assume that the relay will do its job when its
coil is energised, maybe work a fan, or sound a horn.
I am going to assume that you can apply a wire from ground to the
relay coil, or a wire from 12v to the relay coil.
I am going to assume that you don't want the relay to engage
when you apply the wire with 12v to the relay coil.
I am going to assume you want the relay to engage when
you apply the wire from ground to the relay coil.
Whats this bit about 30 seconds ?
Do you want the relay to remain engaged after a 30 sec connection ?
Please set out what you need in simple terms.
If there is some other machine or system that does a similar thing
to what you want, say about it.
Regards, John