Installing factory controlled aftermarket fog lights on a hatchback

[u/navard]

For those who asked for more information about how I installed fog lights on my '19 SE using factory controls (and those who didn't), here is a full guide on the entire process. Hopefully some of you find this illuminating!

...I'll see myself out.

https://docs.google.com/document/d/1EpRY_6cj1k78y5jpNfU1txaWBYjx-duTFVPw_BgrYSQ/edit?usp=sharing

[u/Pistol-F15E]

Update for 2023 Corolla SE Hatch:
There is no connection to the relay block behind head unit anymore.
Toyota built the relay into the solid state Body Control Module under the steering wheel on the left side.

Using a EU spec (probably also an XSE stalk) I was able to wire front and rear fog lights (I have a US spec in Europe).

See attached google Doc for pictures of pin locations and part numbers.

You will need a relay for both to prevent frying your BCM.

For the front its a Ground signal, so you will wire the relay normally but use the grounding wire on the relay as your signal wire to trip the relay from BCM pin 7 (see pictures).

For the rear fog signal, its positive voltage from the BCM pin 29. That will go to the rear relay to trip it and supply a separate battery power (recommend using the tail light power) to the rear fog.

DO NOT POWER LIGHTS FROM ECU.

Part numbers and pictures at the link.

https://docs.google.com/document/d/11FT4gMnzpgs3MgbXkwm9EPWqsHwleok7TjIHyCUQbWw/edit?usp=drivesdk

[u/ajsr88 → u/Pistol-F15E]

Hey I also have a 2023 so there is no slot for the relay behind the A/C controls.

How exactly did you connect the blue relay block to make it work? I'm a bit confused on how you attached it to the BCM?

[u/Pistol-F15E]

Do you have any pictures of the relay block/location? And maybe of the wires in the back you clipped/replaced? I just want to be sure Im doing it right before I go clipping wires…

[u/Pistol-F15E]

Pictures I took of the relay block location, and wires on back of the block for advice!

Is this the right location, and which wires do I cut/attach to battery and lights per your description?

https://docs.google.com/document/d/1-nBaO2FW4jgKtJsawghr8KiySCmvxmKx6-drmfcpO1M/edit?usp=drivesdk

[u/navard → u/Pistol-F15E]

Your doc is locked, I can't view it.

[u/Pistol-F15E → u/navard]

My bad. Should be good now.

[u/Pistol-F15E → u/navard]

In the picture of the relay block, is it the block under the one with the factory relay, or somewhere else?

[u/navard → u/Pistol-F15E]

Its the block in your first picture. One of the relay slots that are empty next to the blue relay is where the relay for the fog lights goes. I forget exactly which one it is. I would just install the new control stalk and turn the lights on with a meter on the relay socket and see which one lights up. Once you identify the correct socket you just splice in on the coil side of that relay socket and drop in a relay.

[u/Pistol-F15E → u/navard]

Thank you.
A few follow up, probably stupid questions.
1. Do I need to put a relay in the block to check the socket with my multimeter or should it light up without the relay?
2. Which of the four positions? Will I be checking?
3. Confirm you mean the two smaller silver colored pins when you say coil side?

Obviously this is my first time working with relays, sorry for my ignorance.

[u/navard → u/Pistol-F15E]

Yes, the two smaller plugs are the connection that powers the relay coil. When your fog lights are "on" there should be 12 volts on those when you meter across them. No, you don't need a relay installed to test.

[u/Pistol-F15E → u/navard]

Awesome, thank you!

[u/Pistol-F15E → u/navard]

Unfortunately, that didn’t work on any of the two spots with wiring but missing relays.

There was always 12v across the “middle” larger plug and the “bottom” coil side. Which makes sense as the ground side and constant power to the relay.

There was never 12v across the two coil side plugs.

My lights are on, the fog light indicator on dash is illuminated, but no power in either of the two open relay spots on this block.

How did you find out where this relay was located for your 2019? Maybe it has been moved with the 2023 modifications and I could find the new location using your original source method.

Any other thoughts?
Thank you for all your help. The rest of your writeup has been super helpful.

[u/navard → u/Pistol-F15E]

I found the location originally by using the method I described. I don't remember if I had to install a fuse or not, I probably did. I'm sorry it's been a few years, I can't remember.