I need to tap into an Under-the-Hood 12 Volt Source that is "Switched". I need the source wire I want to tap into be ON with the Ignition Switch ON and Engine running and OFF with the Key OFF and the Engine NOT running.

This source of 12 Volts will be used to trigger a Power Relay needed for my Fog Lights.
I have the Lights installed with Dual Relays that will allow me to have the Fogs come ON with either High or Low Beams. This part of the Circuit is good. I had the Fog Lights +12 Volts wired directly to a HOT Post on the Top Power Distribution Block.

With a 3-way Switch on my Dash, I could select ON-High / OFF / ON-Low. But the Wire from the Relays to the Switch shorted to Ground ... Leaving the Fog Lights ON at all times.

Solution:
Replace the Wires from the High / Low Relays running through the Firewall and protect them from getting shorted-out by being grounded to the frame where they were squeezed between a Boot and the Frame.
INSURE that the 12 Volt HOT Wire feeding the TWIN Relays from the Battery Post is Relayed and Triggered by a source that is SWITCHED.

Does anyone know ... for sure ... what wire will be 12 Volts Hot and Not depending on the Ignition Switch controlling its ON - OFF status?