""Now, the CORRECT method can be even simpler than the above:
Switched 12-volt power is still connected to Pin 1 on the pump.
Constant ground is connected to Pin 2 on the pump.
The ECU butterfly control wire (Grey wire from the OEM butterfly solenoid plug) is connected to Pin 3 on the pump.
So, when you start the car your switched 12-volt power kicks the pump on. When wired this way, as long as the key is in Run position, the pump motor will function.
Now for the fun part: Your ECU controls the amount of vacuum "seen" by the butterfly actuator by changing the solenoid's duty cycle. It does this by rapidly closing and opening it's ground circuit (grey wire) to achieve a specified pressure at the butterfly actuator by opening and closing the trap door inside the vacuum pump, much like an electronic boost controller controls how much pressure your wastegate sees. Essentially, they "vent" pressure in short bursts to control the actuator diaphragms.""
So this is the way I should wire up the Volvo pump correct? No relay or anything is needed like it shows in the main post of this topic right?