Splicing into the door light switch is a good idea, but the problem is the ignition light would go out when you close the door.
I don't know about you , but I usually close my door before I put the key in the ignition.
What you want to do is wire in a delay that keeps the light on for a short time after the door is closed. You can buy kits from the electronics stores to do this.
Ray.
That's what I was thinking. If the door's open the interior light's on. And if the interior light's on, you should be able to find the ignition key-hole.
Having said that, modern Commodores have a similar delay on the interior light itself, which is quite handy. It's over-ridden once you turn the key or operate the central locking, but otherwise the light stays on for about 30 seconds.
cheers
RET