I want to wire an on/off switch to my aftercooler's waterpump, but I don't know how I would do it.

Would the pump and the switch both have to be grounded?

I would use the switch to toggle the 12v wire, correct?

If somebody could draw up a picture of how this should work, that would be awesome.
I don't want to start a fire under my dash....

Thanks.

well u shoudl have a relay..thast pump will draw way to much through the switch

^^^^^ Believe it. Go to radio shack or maybe autozone and get a 30a 12v DC relay. As you can see in the fabulous MS paint drawing we have on display here you will wire a 12v lead to the switch and one of the NO (normally open) contacts on the relay. When the switched is turned on voltage goes to one side of the coil and the other side is connected to ground. This causes the relay to close the NO contact which sends voltage to the pump. Make sure to fuse the 12v connection going to the NO contact.