Wire courtesy lights to dome light

[Jay11]

1998 Ranger 2.5 Regular Cab
I want to wire door courtesy lights to the dome light, that will light up exactly the same. I see a green, yellow trace (GY) and a black, blue trace (BB) wires at the dome light. I was wanting to tap into the wire loom on driver side, behind the seat, just before where it goes up the wall to the dome light (pic 2). So I tapped a test light into the same wires. Even though the dome light is working just as normal, my test light isn't working. Can somebody assist, what am I missing?

 

[RobbieD]

Put your test light clip to ground. You should see constant +12 volts on the Grn/Yel when probed.

Ford switches positive to the courtesy light. Test light clip grounded, you should see + 12 volts on probing the Blk/LBlu wire, when the doors are open.