I'm installing a A/F gauge, AEM UEGO 30-0300, on ac71 Barracuda 383. I initially wired the power from the accessory feed (yellow 3 port connector) within the under dash harness. The O2 sensor "heats" when turned on, and pulls current.
I don't want this current draw when the engine isn't running. I'm thinking I need to be on the ignition run circuit (blue wiring) to feed power to the O2 sensor and gauge.

How have others dealt with the keyed 12V wiring source? Should I go through the firewall and power from the alternator side of the ballast? Is there a better source location on the dash side?

I think you will find key on and acc is going to power it the same.
I don't know how you would tap it except to relay it through the start run circuit to prevent it from coming on in acc only mode.

OK, Is there a difference in keying to Acc in the counter clockwise direction versus Acc keyed in the clockwise direction? Thanks for the input.

that's what I'd do. tie it into that circuit