I ran mine through the boot near the steering column. There was a small closed off tube coming off of the boot and I used that. It is a pain though because it is so far back under the wiper cowling. I was able to poke a metal rod through from the inside and attach the wire to it and pull it back through.

 

I used an existing boot around an opening, like p220sigman. I used one toward the passenger side; I just found an empty area in it and poked a hole through... having first checked that the interior side would be accessible.

 

Same here. Used one of these rubber boots on the drivers side. I pushed the rod of a metal cloth hanger from the inside through the hole. I soldered the cable to the cloth hanger and pulled it back in.

 

Thanks for the input! I finally got around to doing this and was able to get it through the boot on the driver's side. It took some determination - its really tight in there. I wish i would have thought of the wire coat hanger trick.

 

Just finished mine yesterday. Not sure if it's any different than what the other posters are saying but I used the same harness that the hood release goes through. There is a spare nipple that you can snip off the top and push the wires through. Followed the hood release cable around to the vicinity of the battery.

 

how bout 2015 sienna??

 

same here. trying to install a siren chirper on my 2015 SE.. but i need to find out how to route the wires through the firewall. i really dont want to drill a hole or anything. i wish Toyota had made a designator solely for hooking and wiring things up..