I want to add some new fog lights in, and wondering if I can use this already existing wiring.

Please and thank you.

Yeah, I have my stock fog switch controlling some HID fog lights. Don't splice the lights directly into the current wiring, instead use a relay and have the stock wiring work as the switch.

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Same. Rigid amber fogs spliced in and running off the steering column fog switch. It helps keeping the amount of switches in the rig down so the 4runner doesn't feel like the millennium falcon

Yep, I've got some LED fogs connected to the stock wiring and switch. I snipped the connectors off the stock (ruined) fogs and spliced the new LED fogs into those connectors, and simply connected those to the stock harness. Works great. Since the LED fogs pull less power than the stock halogens there's no need to use any additional relays unlike with HIDs.

Stock fog lights are two H3 55watt bulbs - if you're removing/replacing the stock fogs, you can directly wire HIDs (35W or 55W) or LEDs there and be fine. Hell, you can run a whole 100W+ LED light bar and still be within the factory spec.

How would I go about adding in a relay to the existing wiring?

I found "The One", 2001 Sport Ed. TRD SC'd

This is how I did it on my 01, BFAD's idea. Post #1698.

would I be able to wire it in a way that it would have constant power?

Generally yes. You have to do a mod in or around the fuse box. That change depends on year/options.

Factory wiring only allows the fogs to be on with low beam headlights (off with no/parking/high beams).

-Charlie

What type of mod?/what exactly would I need to do?

For a US '99 model with no daytime running lights, here's the fog light diagram:



The 10A HEAD L/R fuses only get power when the headlights are on (or in flash-to-pass). The 15A Fog fuse has constant power. The R-Y wire is actually connected to the high-beam filament, oddly enough. The Fog relay only will get power when the low beam headlights are on (the relay coil is powered THROUGH the high beam filament).

For any time fogs: Pin 1 of Fog relay can be connected to Pin 5 instead of the R-Y wire
For parking light linked fogs: Pin 1 of Fog relay can be connected to the Green wire that is the output of the "Tail" fuse instead of the R-Y wire.

The actual implementation is up to you - all of the wires in question are in/around the engine bay fuse box.

-Charlie

I have Rigid pods wired directly to the OEM wires, and control them with the stalk on the column.

Mike

That’s exactly my plan here, too.
Did you do what Charlie said and mod it so you have constant power to them?

Do you mean constant power only when the runner is on? If that's the case run the switch from the relay to the acc fuse. That's one that turns on and off with the runner.

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Same. Cut the factory harness, spliced in Rigids. Works like a champ.