Cut off switch wiring

[acox99 74 1 Cars]

So I’ve currently got a hidden pump cut off switch. But I’ve been thinking of changing it so the car will run for X amount of time before it cuts out, but I’m struggling to work out how to do this. I’m no auto electrician and I guess you can’t buy a specific device to do this. I’m wondering if I can somehow wire a timer relay to the tachometric relay that I can switch. But I don’t know how it would trigger if it’s poss to do. Any help greatly appreciated. I know things like this are always delicate in an open forum but I think everyone here is pretty cocha. 

[Spesh 31 1 Cars]

I'm not quite sure what your trying to achieve but you could possibly repurpose a turbo timer to do that? 

[Tom Fenton 1,541]

You could maybe use a timer relay to do what you want, but it really sounds like work for nowt. 

[acox99 74 1 Cars]

I think you are right Tom, I’ve got a bit carried away thinking. If someone wanted it that much it would get lifted I’m sure. Il stick with what I have.