I owe you an apology, you are indeed correct, here's what it says
Connect the red power wire to a switched +12 volt source that maintains power during engine cranking. Most vehicles break the electrical connection to accessories while the
engine is being started. If the boost gauge is connected to one of these circuits, the auto zero function will not work properly and inaccurate readings will result. To determine
whether a switched source maintains power during starting, look for electrical accessories in the vehicle that remain on while the engine is being started. Connect the red power
wire to the same circuit that powers one of these accessories. The connection can be tested by turning the key switch from off to on, the pointer will move backward to the stop
pin and then move to zero. Once the pointer has reached zero, start the engine. If the pointer reads vacuum without returning to the stop pin, a suitable connection has been
found. If the pointer moves to the stop pin and then reads vacuum, another power circuit must be found.
Power-Up
The pointer will move backward to the stop pin and then move to zero. This procedure is an auto-calibration function and is performed on every power-up. While this test is being
performed, the gauge may make a clicking sound. This is normal.
Electronic Boost/Vac gauges are equipped with an auto zero function used to compensate for operation at varying altitudes. This function takes a pressure reading during the time that the
key switch “flies through” from the ON position to the START position. The reading represents zero pressure and is used to set the zero point on the gauge each time the engine is started.
You can get a cranking live feed from the same place as the ecu