Hook up the monitor

Are you looking for a headlight illumination circuit to light the display of a device?

If you are, you will need a test light that shows what wire is hot when the headlights are switched on, and that will usually be attached to the stock stereo.

A wiring diagram for your vehicle would aid you better without stabbing wires to find the one you want, or testing the plug sockets with some bayling wire twisted on the test light.

That would be odd, since most tech these days have a dimmer built in.

So, what exactly are you trying to do?

If you are trying to get power from the dome light.
There should be an orange wire. It will be hot all the time. The light gets grounded to turn on.