Allow Fog Lights to be on without headlights.

Basically, it involves moving the trigger wire for the foglight relay from the wire that's powered only when the headlights are on, to another power source that is powered when car is in Ready.

So you need to know which wire to move, and where to move it to.

 

Factory, or aftermarket add on foglights? If it's factory, you may be able to rig something up in the engine fusebox with the oem foglight relay.

 

State laws vary, so most manufacturers default to only on with low beams which is legal in all 50 states.

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Not sure about that, my Camry with factory foglights only allows foglights on with lowbeams. Foglights go off with highbeams too.

 

It can be legal to have fogs with high beam if the low beams shut off. It is not wise, but legal.

 

Not according to my 2012 Liftback manual. Page 257, they work only with the lowbeams. (My trim doesn't have them, so I can't test to verify it.)

And not on previous family cars with factory foglights. With low beams only.

Fog-lights-only mode is not 50 state compliant, so I haven't been aware of them as factory equipment, only DIY.

 

Either they're aftermarket foglights that are wired that way, or could you possibly be confusing the LED DRLs on the 2012 - 2015 liftbacks for foglights?

Most Prii do not have foglights, only the level five has factory foglights. If you're seeing a lot of Prii with "foglights" on without headlights, then it's probably the DRLs.

 

If he sees mine out on the street, it is very definitely the LED DRLs that were added with the mid-cycle refresh for 2012. Their light pattern is completely and utterly useless as real foglights. But they will suffice for those who use 'foglights' merely for cosmetic and decorative purposes, not for foul weather vision.

Squeakasaur: Look at xliderider's avatar picture, of a 2010-11 model. His round lights directly beneath the turn signals are foglights.

2012-15 Liftbacks have a more triangular lens (when unlit) there. When lit, it is a square pattern of 4 LEDs. These are DRLs, not foglights.

 

Depending on your model the c is pre wired for fogs. All you have to do is buy the fog light kit and add the stalk from a c4. I've got the parts, just trying to find the time to install.

 

Hmm that sucks .. unplug from the harness and run new wires to your own switch? I have a 3 and my kit came with separate wire/switch. But the switch is ugly I was going to try and avoid using it.

 

I got the kit too, used the factory harness, but use the button instead of stalk. Too much of a hassle to remove the steering wheel.
It is possible to bypass the OEM relay if you just want the fog without the headlight on factory. But it will have to be a switch, the stalk requires a double connection to turn on the fog. That means there's no closed circuit when you set the fogs "on" on the stalk till you turn on the lo beam.

 

There is a detailed section in Priuschat on how to do this. I have done this on other cars, and it is no fun. Finding the right line to tap into is a pain. Then, usually the juice needed to run the fog lights on the same circuit causes quite a load, so you will have to get some heavy gauge wiring. Then you have to get a switch heavy enough to carry the amperage or it literally melts the circuit together, causing that oh so familiar "something electrical is melting smell". The fastest, easiest way to do it is to find the ignition power line, tap into that, ground it and have it on its own circuit with your own on/off switch. But, there is a dictionary in here on how to wire it the way you want, it will take time. And please be careful!!