If you wire the lights to come on with the parking lights, use a relay. The parking light circuit may not handle the extra load by itself, I think it is only a 10 amp circuit anyway. Use a Bosch 12 volt 30 amp relay and tap into the black/yellow wire at the headlight switch, connect that to terminal 86 on your relay. Connect terminal 85 to a good solid clean bare metal chassis ground. Connect terminal 87 to 12 volts fused at about 15 amps, maybe more or less depending on how much current your new lights draw, and then terminal 30 connects to the positive wire on each of the new cab lights. Be sure to fuse the 12 volt positive wire, within 6 inches of the point where you make the connection for power, like at the positive battery terminal. This will prevent a fire if the wire ever shorts to ground.