I want to install some reverse lights on a backrack I want them to be able to come on when I switch to reverse aand I want them to be able to turn them on manually . Some told me I need a relay and a special switch. Can someone tell me what I need and help me with a wiring diagram?

 

Here's a diagram. You need to buy a Bosch type foglamp relay. Add your switch from the "coil" wire to the "common" wire. This will make them come on even if you are not in reverse.