reverse light add owiring diagram

I am looking for a diagram that will illustrate the following. I wish to add an additional utility light to the rear of my 2005 dodge grand caravan for night time visibility when backing up. I want the light to go on when the vehicle is put into reverse. I also want the light to go on by an illuminated switch when the van is not in reverse. This will allow me to have light at the rear of my van when doing work there. I have read that a diode will need to be wired into the circuit so a diagram of everything would be most helpful. I think my reverse light wires are white and light green.The add on light should be able to go on when the van key is in the auxiliary position that way I don't accidently drain my battery.

Try with a relay. WHITE/ l.green (+)from car to 86 ground to 85 acc wire 87 utility light 30.