Fog Light Wiring for Tacomas Without Fog Lights

Hello, fellow Tacoma enthusiasts! Recently I installed some aftermarket headlights on my base model Tacoma, which created an issue where my aftermarket fog lamps would remain on when my high beams were activated (my Tacoma is not factory wired for fog lamps, but I have OEM style aftermarket fog lamps). I know a lot of people here would consider that a plus, but I prefer to keep the fog lamps functioning properly, so I thought I'd do a write-up with all the info I've learned and the schematics I've come up with. For the sake of those who are new to aftermarket fog lamps, we'll pretend from this point forward that I'm installing them from the ground up.
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I thought I'd share a little bit of information for the next guy who decides to install fog lamps on a Tacoma that isn't already pre-wired for fog lamps. I have a 2013 2.7L Base Model Access Cab that was not pre-wired from the factory, but the bezels were present on the bumper with ugly caps in place of fog lamps, so an aftermarket install was a must.

I chose to purchase the Toyota LED Upgrade lamps that are offered as an OEM upgrade to the original halogen lamps on 2016+ models. Yes, my Tacoma is a 2013, but the 2016+ lamps fit right into the bezels on my 2013, but will not fit anything before 2012. The part number for these is PT413-42190 for the aluminized bezel, and PT413-42191 for the black bezel.

You will also want to purchase a wire harness for your fog lamps if one is not included; preferably, you'd purchase one that comes with an OEM style dash switch. The one I used was similar to this:

Ricoy H11 880 881 H8 12V 40A Relay Wire Harness Kit With LED indicators Switch ON/OFF For Toyota Lexus Driving Fog Light

https://www.amazon.com/Ricoy-Harness-indicators-Aftermarket-Conversion/dp/B07M83TX4G?crid=A337SMUG1SET&keywords=toyota+tacoma+fog+lamp+wire+harness&qid=1691296952&sprefix=toyota+tacoma+fog+lamp+wire+harnes%2Caps%2C178&sr=8-5

This particular harness includes the switch, a built-in fuse holder with a 15 amp fuse on the positive lead, and a SPST relay (this is important because you don't want to run power to your lamps directly through the switch). It also has two H1 connectors that will connect directly to most OEM style fog lamps. With some LED lamps, it may be necessary to reverse the polarity on these connectors (switch positive and negative around)

Now, the end goal for me was to have fog lamps that look and function like OEM lamps, so the wiring schematics I'm about to show you are designed for the fog lamps to operate ONLY when the low beam headlights are on. Some people modify their OEM fog lamps to operate independently of the headlamps, and it would certainly be easier to wire aftermarket fog lamps independent from the headlamps, but for this example, I'll be demonstrating how to do it the legal way.

First off, you want to disconnect the negative battery terminal before you do any electrical work on the vehicle.

The wire harness I provided a link to has two positive leads (red, blue) and one negative lead (black) with ring terminals on the ends. The red lead has a built-in fuse holder with a 15 amp fuse pre-installed (I swapped it for a 10 amp because LEDs draw less current than halogens) and will provide power to the fog lamps themselves. This wire is connected to pin 30 on the relay, which when activated by the switch (relay pin 86), outputs on pin 87 to the fog lamps. The black lead will be the grounding connection for all components in this install. The blue lead will provide power to the dash-mounted switch for illumination, and provide power to the relay on pin 86.

The red lead can be installed directly to the positive connector on the battery, under the alternator strap.

The black lead will be the main ground connection for everything in this setup—the fog lamps, the relay, and the switch (which is grounded for illumination). You could, in theory, connect this straight to the negative battery connector (under the 10mm bolt) but I would recommend connecting this where the main grounding strap directly next to the battery attaches to the body of the vehicle, to avoid the potential wear and tear of repeatedly unhooking the negative battery connector and stressing the ring terminal on the wire harness.

The blue lead on the wire harness will vary for different situations. In most cases, you'll want to connect this to one of the low beam fuses, in the main fuse panel under the hood, via an add-a-circuit fuse tap. The reason you'll want to connect this to the low beam fuse is so that the switch is only receiving power when the low beams are activated. There are several reasons for this: the first reason is that most states have laws against driving with only the fog lamps illuminated. Secondly, by connecting this to the low beam circuit, you won't have to worry about turning off the fog lamps when you exit the vehicle, as they'll turn off when the headlights turn off. Additionally, if the switch you're using is illuminated, you'll want this connected to a controlled circuit vs an always on circuit or the battery, because you don't want this light to stay on when the vehicle is off. If you absolutely must have your fog lamps operate independently from the headlights, you can connect this blue wire to one of the ignition-only fuses in the passenger compartment fuse panel. Either way, you'll want to snip the ring terminal from the blue lead and either solder or use a butt connector to connect it to the desired location. Most add-a-circuit fuse taps come with a pre-crimped butt connector on them, and you'll need a crimping tool/wire stripper to crimp your blue wire to this.

I'm about to show you two different schematics. The first one applies to most of you with OEM headlights, or any aftermarket headlight that maintains the single dual-beam bulb design. In this scenario, the low beams and the high beams operate separately, which means the low beam circuit actually turns off when the high beam circuit is active.

In this example, the fog lamp switch (blue lead) is connected to either the Low Beam LH fuse or the Low Beam RH fuse with an add-a-circuit fuse tap (7.5 A) in the main fuse panel under the hood. With this setup, the fog lamp switch will only function with the headlights in the low beam position. Because the low beam circuit turns off when the high beams are activated, the fog lights will automatically turn off when the high beams are activated. Additionally, the fog lamps will not operate when the headlights are off, for the reasons stated above.

Now in my case, I have the Morimoto XB LED headlights, and those headlights have an internal circuit that bridges the low beam and the high beam circuit, so that the low beams remain illuminated when the high beams are on (this is an upgrade over the OEM headlights with the dual-beam bulbs, because you don't lose the illumination directly in front of you when you activate the high beams). After I installed these headlights, my fog lamps would remain on when my high beams were activated, because the high beam circuit was energizing the low beam circuit. To solve this problem, I came up with this alternative schematic, that uses an additional relay to interrupt the fog lamp circuit when the high beams are activated.

As you can see from the schematic, the additional relay is meant to interrupt power to the fog lamps when the high beams are activated. It is crucial that this additional relay is either a 4-pin SPST N/C (normally closed) or a 5-pin SPDT (has an additional pin 87a that is N/C) because we want power to the fog lamps to remain uninterrupted unless the high beams are on. If you're not familiar with the terms normally-open and normally-closed, most 4-pin relays you would buy at AutoZone are normally-open, which means the circuit remains open (off) until the relay is activated. A normally-closed relay does the opposite—the circuit remains closed (on) until the relay is activated. A 5-pin SPDT relay does both of these: the 87 pin is normally-open, while the 87a pin is normally closed. You will be more likely to find a SPDT 5-pin relay than a normally-closed 4-pin (SPST) relay at your local auto parts store, so that's what I used for my application, i.e. just look for a 5-pin relay.

In this schematic, I've added an additional add-a-circuit (7.5 A) to the high beam fuse in the main fuse panel under the hood to control pin 86 on the additional relay. The red lead we hooked to the battery earlier in this write-up is cut so that the fused side is connected to pin 30 of our additional relay, and the other side is connected to pin 87a so that it continues to carry power to the main relay until the high beams are activated. Pin 85 is connected to ground (this can be spliced into the black wire on our wire harness). When wiring the additional relay, you can either solder directly to the pins on the relay, or you can use crimp-on quick disconnect connectors. Either way, it is important to tape over all the positive connectors so they do not make contact with any negative connections, such as the vehicle chassis.

Hopefully this write-up is helpful to anyone either installing aftermarket fog lights for the first time or dealing with the same issue of upgrading their OEM headlights and causing issues with their aftermarket fog lights. I know I probably missed a few things in this write-up, so please feel free to chime in with any additional advice, or to ask me any questions about the schematics I've provided. Also, please note that the wire harness I've provided a link to comes with a 15 amp fuse pre-installed for halogen fog lamps, but I've swapped mine out for a 10 amp fuse due to the lower current draw of my LED fog lamps, and that's what you'll see in the provided schematics.