Need 18A of power for under-car lighting. Where do I look?

18 AMPS?!?!

You'd better look in your state's DOT regs for auxiliary lighting.
That's enough current to power airport runway lights, and in some parts of the country they're really starting to crack down on some of the more egregious lighting mods.

I actually love it, since it makes me a much less interesting driver.

Make sure you fuse it at 20a and use a good quality 14-16 AWG wire, or you may find out why the kids down at the install place get to charge so much.

Be careful.....Priuses have a notoriously weak 12v (aux) battery. You may want to upgrade the OEM battery as well if your 2010 is still thusly equipped, and invest in a pocket charger.

Good Luck!

 

A good place to look is in the Electrical Wiring Diagram Manual for your car on techinfo.toyota.com. It will give you a huge amount of information on what circuits are available, what they are already fused for, what loads are already on them, what relays and upstream fuses are supplying them and what their ratings are ... plus the wire colors, connector shapes and locations for any of the connection points you decide you might like to use.

For example, in my Gen 1 I could see that the instrument panel fusebox has a couple of fuse slots open and what looks like a relay socket, but of course all its internal connections are invisible. From the wiring diagram manual I could learn that one of the fuse slots and the relay socket are already wired so I could add a separate relay controlled circuit that would be powered in ACC position, and the other unused fuse slot is powered whenever the rear defogger is, and could be used for heated mirrors (even though those weren't offered for the car). Of course the manual even identifies the connector terminals where those circuits come out on the back side of the fuse box. There really isn't any other place I could have looked up useful information like that.

As for later Prius generations, I can't predict what similar easter eggs you could find waiting for you in your wiring diagram, but it is chock full of useful information and any time you want to integrate new electrical stuff into your Prius, it is a very good place for your planning process to begin.

-Chap

 

Go straight to the AUX battery terminals....

 

Under a small cover in your engine fuse box, there is a bolt, where the heavy gauge wire from the 12v auxiliary battery comes into the fuse box (seen here in this pic where the screw driver is, a cover has been removed, top center of this pic, to the right of the heavy white wire). You can put a ring terminal under that bolt, but be careful, treat that bolt as if you are working on a live 12v power source (which it is). This bolt is powered, even when the car is ignition off!!! Disconnect the 12v auxiliary battery in the hatch before messing with this bolt. The wire you are connecting to this bolt can be fed up into the area from the bottom of the fuse box. Make sure you have an appropriately rated fuse on whatever wire you use to draw power to your controller!

 

I do not think any of the fuses exceed 30 amps.
the HV battery can produce 125 Amps, but you do not want 201v DC

What made you decide to lower the MPG of one of the most fuel efficient vehicles, anyway? it will be a 1/3 HP drain. 250 watt of power, very dangerous. You go first.

 

There are 20 and 30 amp fuses visible in my pic above (post #7). the bolt attachment point (discussed in post #7) is capable of supplying the OP's 18 amps, as it supplies power to the entire fuse box.