Voltage Drop

OK, you can easily check. Really, your top suspects are

the bulkhead connector

the ignition switch connector

the switch itself.

Just check all of them the same way. 1/2 volt is too much. It won't keep the car from running if it is ALWAYS 1/2 volt, but that may change, because a bad connection that causes that voltage drop usually is corroded, loose, and heats up, etc. So sometimes it may get worse, or lose connection all together.

OK----you've checked out in the engine bay, now check at the ignition switch connector, because that's easier than probing the interior side of the bulkhead connector. You can access the ignition switch connector under the column, and "back probe" both sides of the connector.

You can have low voltage coming in on the battery feed TO the switch connector, drop INSIDE that connector, drop in the switch itself, or in the connector again going "out" to the ignition feed

So check voltage with the key in "run" on both sided of the connector at the battery feed. If voltage is down TO the connector, you have a bulkhead connector problem, etc.

If voltage is the same at the switch side of the connector at BOTH the battery infeed, and the "ignition run" terminal, then you have no problem in the switch.

I've forgotten---what model year is your car?