09 Taco?
1. Open hood
2. Look at the passenger side firewall about 8 inches from the hinge - here you will see a small firewall plug. Remove it.
3. Open and remove the glove box (it just pops right out, be careful with the piston arm and remove the box and arm as one).
4. Take a dowel or bit of coat hanger wire and tape the end of your wire to it.
5. Pass this through the firewall and find it behind the glovebox location inside.
6. Run your wires, connect and test.
7. Re-seal the hole in the firewall using: a. modified firewall plug, or b. RTV silicone and rubber grommet. Do not allow the wire to chafe against a metal edge anywhere.
8. Enjoy!
Note: On 05+ Tacos there are two really good locations to pass through the firewall on these trucks, the one described above and the drivers side where you will see the main wiring harness pass through. The passenger side is less cluttered thus easier to work with IMO.