If you don't mind that the pump is running all the time that your vehicle is running, the answer is rather simple. If you only want the pump to run from the time you turn the ignition off and then for a minute thereafter, it is a little more difficult, but not by a bunch.
In the first case, you use a transistor (a darlington to get the base current into the microamp range) to turn on the relay and a resistor with a large capacitor to create a one minute time delay. Run the base of the darlington to the capacitor through an appropriately sized resistor and that's all there is to it.
Let us know if you only want the pump on at the time you turn the ignition off.