Keyed/ignition source under the hood??
 

Getting ready to start the re-wire of my 67 Bird. All new harnesses. Since I'll be using gauges that have built in warning lights for oil pressure and water temp the stock wires for the original sensors won't be used. Looking at the wiring diagrams it appears that the sensors were a ground source for the factory warning lights. If this is true wouldn't those have a 12 volt ign/keyed source I could use as a trigger for a relay??

Yes, and no. The bulbs in the instrument cluster have 12 v + to them.
Like oil pressure, and hot light. They come on when the sender grounds the circuit coming from the cluster.

If you need a simple wire to use to power a relay coil, use the windshield wiper feed power wire.
What are you wiring?

Coil is ok. The initial item is halos for DRL. Don't want to splice into any wires being used such as the wipers. Which is why I was thinking about the water temp or oil pressure leads. But seems like the power actually goes through the bulbs then to the sensor. Which makes sense. Since I won't have that path to use I guess I can look else where. Or maybe use the coil feed. Forgot about that one.

You should have the halos come on with running lights, no? You can tap into a running light wire by the core. That would be the least amount of wire to run, you could tap each side into each front running/parking light.

If you didn't want to actually tap into the harness, you can pull a terminal out of the connector, cut it off, and crimp a new one on with an additional wire for the halos. If you want to get slick about it, use a single pole weatherpack connector.

They are LED? They won't draw much power then.

If you think you're going to need multiple key-on 12v sources, you can use a relay, a key-on trigger, and mount a small post for feed. Then any time down the road you need to add a key-on power, you just run it to that post.

I personally don't care to run anything off the ignition power wire, there's future possibilities of feed back, and you may get run-on. Or low voltage to the ignition. Keep that isolated.

Another possibility is if your harness is wired for cornering lights, you might be able to use that. You can buy the associated Packard connector and make it look OE.

.