Newbie Question (foglight install wire tap)

I don't have a Prius c, do you have auxiliary terminals in your fusebox like the Gen 3 Prius (where the two red wires are plugged - in here)?

If you don't have these terminals, use a fuse tap to tap into an existing circuit in the fusebox.

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When doing that project on my Gen 3 liftback, I got a little unexpected reward for looking in the wiring diagram, that came in the form of finding the instrument-panel junction box already contains a fog light relay and fuse, and all I had to do was wire to the right pin number on the output, and connect a switch to the existing input.

I don't know if it's like that in a c, but the wiring diagram will know.

-Chap

 

There should be a fog light fuse in the driver side knee fuse box that I would add-a-fuse into, since you'd need to run wiring through the firewall into the cabin anyway (for the fog switch/button).

The green wire on the fog switch/button (to power the switch), I would probably also add-a-fuse into a 12v acc that's only when the car's on.

Read/look at your manual of the fuse slots, you should have a good idea of where to add-a-fuse into (make sure to get a low profile add-a-fuse, so you can close your fuse panel cover back up (I left my cover off for the longest when I had my seat heaters add-a-fused into the seat heater fuse slots)

I wouldn't tap/cut/solder/etc into any factory wiring, just because I suck at doing a good job and I just don't like doing things that are permanent-ish.

Add-a-fuses are very forgiving, while cutting/tapping into factory wiring isn't so forgiving in the long run.

 

dble pst

 

I didn't cut or tap any factory wiring ... just plugged into it.

-Chap

 

The foglight indicator in the instrument cluster illuminates when foglights are On?

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Yes, but it's a low current one that just powers the switch illumination, and the trigger current for the relay coil.

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I tapped the sunroof fuse (I don't have a sunroof) in the fusebox below left the steering wheel for power, and installed a switch (powered by accessory) that would power the relay that gave power to the fogs. I routed the power through the firewall by following the hood release cable that passes above and aft of the front drivers side wheel. I've attached the guide I used to get through the firewall. In short, you just need page 3 of the pdf. IMO the hardest part was just getting power to the fogs.

 

Huh. Interesting question. No, I've never had a dash light. Sure enough, the owner's manual shows one:

("if equipped", it says), but TBH, I think several of those icons are missing from the stencil in my meter. (Shining a bright LED flashlight straight at the display when it's off, you can barely make out what icons are there. I didn't try to take a picture because I don't have enough hands and the outlines are so faint it would probably not have come out.)

When I enter the Techstream combination meter active tests, it also doesn't have an "Indicat. Fog" test. Just one for "Indicat. HEAD" and one for "Indicat. BEAM".

So I guess there are different versions of the combination meter. Everything else about the foglight system works as the owner's manual says ... the fuse and relay are already built into the IPJB, you just ground the right Body ECU pin with a fog switch and the relay clicks (when the low beams are on), and the power comes out on the right IPJB pin.

I wouldn't be surprised if exchanging the meter for one with the fog indicator, it would light up. But it's a pain to switch the combination meter, because of the odometer.

This is all Gen 3 liftback though, not a c.

-Chap

 

I wired mine with the 12v white wire to “25A s/roof”, and the green trigger to the “15A cig”. Give that a try.

I believe why the “15A fog” wasn’t working is you likely don’t have the factory fog switch, which I’d figure needs to be turned on to enable power to “15A fog”. Regardless on what was powering the switch, enabling the relay, the relay had no power to pass to the fogs.

 

That grounding point seems fine. To be sure grab a multimeter and check continuity between that grounding point and a known good negative, say the side wall of the cigarette adapter. From there, when you press the switch, listen for the relay engaging. There should be an audible click when it does. If you don’t hear it, check that the switch (green wire) is hooked into a known working power with a multimeter. If you do hear the relay engaging, check that the fog power (white wire) is hooked into known good power with a meter as well.
With the way mine is connected, accessory power is only on when the car is on, but the sunroof power is always on regardless. Something to keep in mind while troubleshooting.

 

I have a trim 2 and for me it was. Best to be sure though and test with a meter.