I installed a dome light in my hatch, but i want it to turn on automatically with the hatch door opening. There are a few wires running to the hatch handle, but before I start splicing into them has anyone tapped the power from the hatch like that?

 

Looking at the schematics, it does not look like there is a "constant" hot in the hatch. area at all. Unlike many older cars, Scion typically switches the ground, rather than the hot.
I installed my rear dome light in the roof, but the same wiring could be used. I ran my hot (T-tap) for the my rear dome light from the constant "hot" (Light blue-yellow stripe) at the OEM dome. (use an inline fuse 2 Amp for extra protection) This hot could be run through the rubber boot on the right side of the hatch to your rear dome light 'hot" you are mounting in the hatch.
After you tie the hot into the rear dome, run a wire to the switched ground (red-white stripe) with T-tap for the hatch light. This wire also goes through the rubber boot on the right. Make your T-tap in that area, because somewhere in the hatch ( I didn't look that deep), even after it goes through the "switch", it is still red-white stripe which would keep your light on all the time.
So, when you open the hatch, the rear dome will light, along with the OEM dome in the center. When you close the hatch, the hatch dome will go out instantly, but the other will slowly fade out. I kept the rear dome out of the auto-dimming circuit because I did not want to take a chance of overloading the auto-dimming circuit board.
This will isolate the rear dome to just the grounding wires. With this wiring, the rear dome will light whenever the OEM dome light lights (any door or hatch opened)
If your rear dome has an "ON" positiion, like the center OEM dome, you will need to tie that wire from your rear dome light direct to ground, in the hatch (under a screw nearby)
If you only want the rear dome to come on, then it would probably need its own switch (mercury perhaps) that "knows" when the hatch was opened, but still could get the hot from the OEM dome.
Hope this helps. Any other questions that I can perhaps help with, post to the original post, or send me a PM or e-mail.
I have had my rear dome in operation for about 2 years now, and no problems. Love the light it gives back there. I ended up also installing map lights, up front, and a switch and relay that would allow both map lights to come in with the rear and OEM dome light. And still have the ability to use the map lights individually.
Enjoy the BOX.

 

Wow. Awesome reply. I have already ran a power wire through the boot in the hatch, so I guess I'll run another. Thanks!

 

If you have already run a hot into the hatch, you could just T-tap off of that to the hot on dome. And then still use the switched ground (red/white stripe). Let me know how it all goes. Are you mounting the hatch dome in the same location as the upper brake light, but just on the inside? You will definitely enjoy the light that the rear dome gives. Enjoy your unique BOX.

 

Ok, I see how that will work, but the problem is I have the power wire hooked to a switch right now, So even in the case of using the switched ground, ill still have to redo the whole circuit.

The light itself is on the plastic cover on the hatch. It's out of an escort from the junkyard, ill try to post pics, I havent painted it yet though.....

 

Then, take the hot from up at the OEM dome. I got my rear dome from an old Honda, and front map lights are out of an old Mazda. I think they cost me around $4 for both. Cheap mod, and one of my favorites. Stay as much as possible with the DIY, (or PE) as I prefer, and you will appreciate the BOX even more.

 

I just did this mod yesterday. The wires to the latch are of no use. They control the latch servo and detect when the latch is in the closed position. To do it properly, you will only need to run two wires along side the wiring harness and splice them to the dome light wires. You will find them hidden behid the C pillar. The red is the door circuit (negative) and the blue is the positive. The second ground can be grounded to the little bolt on the wiring harness.

 

My original post (I realize it is long) did not recommend using the latch wiring. The two wires going to the OEM dome are Hot (light blue/yellow stripe, and the red/yellow stripe which goes through the door lock control relay and the dimmer circuit. I used the Red/white stripe going through the hatch boot as the switched ground (auto dome light)(it does not go through the auto-dimming circuit. Hope this helps. I have drawn out my circuit mod (updated OEM wiring schematic), and mine has been working for over a year. You will need to ground one wire off the switch to the metal hatch if there is a "manual" ON position also.

 

 

Sorry about the previous post. I had the polarity backwards and could not get the lamp to operate correctly. I have now corrected the post to show the correct wiring (see my previous post this thread). Sorry about the goof.