UltraGauge does not power on when connected
The OBDII connector not only provides a communication path for UltraGauge, it also supplies UltraGauge with power. The power is always hot and drawn directly from the battery, the position of the ignition switch is not a factor.
The power at the OBDII connector is fused. Sometimes there is a dedicated fuse for the OBDII connector, but more often the OBDII connector shares a fuse with another circuit or circuits like the horn, windshield wipers, instrument panel, power windows, etc. The actual shared circuit varies from vehicle to vehicle.
Its not uncommon to find that UltraGauge does not power up when initially attached, only to find later that the horn, which stopped working months ago, was the result of a blown fuse which also prevented UltraGauge from powering on.
As a test, attach UltraGauge to a second vehicle. If it powers up in the second vehicle, then there is a good chance the first vehicle has a blown fuse or damaged or corroded OBDII connector.
Vehicle's female connector. Pin 16 is battery (+12V). Pins 4 and 5 are ground.