Best way to wire foglights (to headlights)

You can tap into the brown wire under the dash like in the instructions, if that is still applicable to the '12 model year, and leave the switch in the on position. The brown wire will power the relay to activate the fogs.

Or, if you don't want to go through the firewall, which it sounds like you don't, then you can tap either a parking light or low beam headlight + wire to activate the relay.

 

Me and another user came up with an all-under-the-hood solution for fogs on w/lowbeam off with highbeam. Simply search for "foglight" with my user name. If you can't find let me know.

 

Ah does that mean you found the thread or need it?

Anyway, here is a link to the diagram:

2010 Prius OEM-quality Fog Light Kit Now Available! | Page 24 | PriusChat

Also, here is a link to my two relay solution.
http://priuschat.com/attachments/foglight-diagram-pdf.36334/

 

Those diagrams that spiderman linked to are perfect.

If you don't need the high beam cutoff, eliminate the second relay and connect the tap from the low beam purple wire to terminal 86 on the relay.

 

OT, spiderman what program did you use to diagram that setup?

I have sketched out my project to wire the high beams as DRLs, with a low beam cutoff, but I haven't found a good program to diagram it. Free would be good

 

Ooooh, highbeam DRLs... with reduced intensity? Kewl.

I downloaded a free-trial program just for that project. I can't remember what it was, sorry.

 

Yeah cool, it uses either 4 SPDT/1 DPDT or 2SPDT/2DPDT relays to accomplish switching between half power high beam DRLs in series and full power high beams in parallel, with an automatic cutoff when low beams are turned on.

I'm already gathering up the relays, wires, diodes, and fuse holders for my project.

 

It's important to remember that running your fog lights combined with your headlights when bad weather doesn't require it is illegal in many states... I'm sure we all know what it feels like to have some jerk with high beams on and way too bright vehicle lighting system nearly blind us when they come up from behind us on the highway. This is not only unsafe to the driver you're following because you're limiting their vision, but in many case it's illegal... I once paid a $230 fine for this in California...

SO ALL YOU PEOPLE OUT THERE THAT THINK HAVING MEGA-BRIGHT HEAD LIGHTING AND FOG LIGHTING IS GOOD, SOONER OR LATER YOU'RE GONNA REALIZE WHY IT CAN BE REALLY BAD TOO!