Why do you keep talkin about relays. they are different than switches. Relays are "automatic" switches. the whole point of using a switch is to manually overwrite what your PSU is automatically doing.
these are examples of SPDT switches. They have 4 terminals and can be set in 3 positions (left, center & right).
so i don't get the point of you using a relay (your PSU already uses one, taking IGN as a input)