E30 Zone

What's the best way to get an ignition switched 12V into the boot of an E30 M3?

I don't think any of the lighting circuits will be switched, but is the heated rear screen?

I only need it to trigger a relay so very low current requirement.

Thanks.

Rear screen is fed from an accessories (switch posn. 1) switched 12 volts, but this is only fed to the rear of the car when the screen is on.
Brake lights are ignition switched live, but again, only fed to the rear of the car when they are on.
The nearest usable thing to an ignition switched live at the rear of the car is the fuel pump feed, which is live when the ignition is on, but only with the engine running.

What are your plans as it may open up more options.

I've decided I'll take a wire through to the dash as it's easy enough to do, thanks for the comments.