How to enable relay when engine is on

[jimv]

HI all,

I would like to have a source of power that is only available when my engine is on, similar to the 'ACC' (accessory) fuse bank in a car.
I'm thinking I would set up a independent fused circuit that would run through a normally open relay, and energize the relay via the ignition (similar to what Brian B mentions in this post.

... I know I have relays operated off my ignition circuit. I installed an additional relay this winter when to power my water flow and exhaust temp alarm. The power for this system is from the fuse panel. The power lead goes to a relay. The relay is activated by the ignition. The relay supplies the alarm system 12V from the fuse panel. As long as ignition is on the relay is activated.

I get that I may be overlooking the obvious, but what signal/source is used to energize the relay?? Do you just tap off one of the pins of the ignition switch?
On my Yanmar 4BY-180 engine, one of the connectors from the ECU (X1) has a pin (G) that is for "power for accessories" - this is part of the wiring bundle that goes to the helm. Is this signal the correct one to use? does it terminate someplace 'handy' up at the helm station?

This may be a simple issue and sorry if I'm not getting it, but any guidance is appreciated.

Jim