Aftermarket Fog Lights wire question

Hello all,.

I’m hooking up some aftermarket foglights in my father in law’s Rav4. The wiring harness didn’t come with instructions. I have everything booked up but got stuck with a few wires and was hoping someone here could help. I have a yellow, white and black wire I’m not sure about. 1 should be continued power, one must be ignition and the other a ground. Tye green plug is for the switch in side the cab. Attached a photo. If you have an option on which wire is what please let me know.


Do some googling , maybe you can find the schematic or at least instructions. If not that, then contact information for somebody to phone. It’s going to be difficult at best otherwise. And if you make a wrong guess, you could damage something expensive to repair.

This is the kind of info you need at the bare minimum: Are the fog lights the type that are either on or off, nothing in between? Under what conditions do they turn on? When the engine is running? When the key is in the “on” position? Only when the headlights are on? Only when a separately installed dashboard switch is on?

The fog lights turn on with a push of a button that came with the lights. The green plug on the wire harness plugs into the switch. Need to push the button to turn in the fog lights or off.

Sorry do a bunch of googling but couldn’t find much that has the same colour wires I needed info on. Or the same harness.

I don’t know how well you get along with your Father in law but my rule is I don’t do anything to some elses vehicle unless I am absolutely sure of the proper result. The phrase ’ Kill the messenger ’ is quite similar to ’ Why did you mess up my car? '.

Do you want the fog lights to turn on anytime you want them, with the press of the new switch? Like even if the key is removed?

I agreed VOLVO_V70. I was hoping it wasn’t a highrixh thing. Lol. The rest of the hardness is plug and play. It’s just the 3 unknown wire which need to be power and ground, but which is which.

there’s only one kind of ground, but there are various types of power to tap into.

  • Always on.
  • On when the key is in “on” or “acc” .
  • On when the headlights are on.
  • On when he engine is running.
  • Etc.

Hey George-San-Josr1,. I’m think no lights if keys not turned, less chance of leaving them on.

So On when the key is in “on” or “acc”

When I decided to install aftermarket driving lights on my tC, also a Toyota product, I did some research first. I tracked down both the wiring diagram AND the schematic (two different documents) to determine exactly how the dealer-installed optional driving lights would have been connected. The schematic showed me exactly how the OEM harness was wired to accommodate the driving lights, as well as an additional necessary wiring harness. The wiring diagram showed me exactly where all the plugs were located.

I discovered that there was the aforementioned additional 3-way harness plus a relay. I tracked everything down right to the physical configuration and part numbers of the plugs… which I then learned were not available from Toyota for purchase. I researched in electrical plug sites, but the plugs were apparently “bespoke” (proprietary) and not in the standard industrial catalogs. No great surprise there.

Bottom line? I was able to use aftermarket lights, but to wire them in properly I had no choice but to buy the wiring harness, and the relay from Toyota… I went ahead and bought the switch too. It was worth it. Everything works properly, and no “electrical ghosts” took up residence in my car.

My recommendation to you is to ask the dealer parts guy nicely for a copy of the wiring diagram and the relevant schematic. That’ll give you all the information you need to properly get everything wired. Bring a good camera with you when you go… if he can’t print the documents you can try photographing them from his monitor if he’ll let you.

In future, I’d suggest doing the research before ever touching a wire. You’ll save yourself a lot of grief. :slightly_smiling_face:

Good luck.


I regret buying them and when I bought the kit it was labeled for the correct car. It’s just wasn’t as plug and play as I liked. I figured that due to having the switch, relay and all plugs rewired that the last remaining wouldn’t be so had to figure cause d so much damaged if hooked up wrong. I was thinking worst case would be they just wouldn’t work. But I’m not much of a wire guy.

Actually, the 'worst case" would be electrical ghosts taking up residence in the vehicle… and that happens more often with aftermarket stuff than most people think.

I’m going to stick with the recommendation to try to get the vehicle’s wiring diagram and schematics.

One rule of thumb I follow when installing aftermarket electronics… if the directions say I have to cut an OEM wire harness… I return the item for a refund. I never butcher an OEM harness. Modern cars have pathways integrated into their harnesses to accommodate just about anything without chopping up the electrical systems. You just need the right documents. And often an extra part or two. I DO, however, use “adapter plugs” where necessary. I’ve had good success with those.

Sounds like I’ve lost. Thanks everyone. I’ll see about getting a OEM harness.

Why not just call an auto accessory place and see if they will connect those wires for a reasonable price.
I wanted an extra power point for a portable GPS in one vehicle and they did it for a reasonable price.

An auto electric shop can probably figure it out for you. it’s just a couple of light bulbs after all. They’ll look up the appropriate reference wiring information first though, so that the lights work the way you want them to work, and the circuit is protected by fuses/relays so no other function in the car is affected. Suggest you don’t proceed on your own without a pro giving you some hands on help. The advice above to abandon this effort and obtain the proper wiring harness from Toyota is probably the most practical solution. There may be alternator implications btw.

Why would you mention turning on the fog lamps regardless of headlamp position, even with the ignition off?

Why are you even suggesting that . . . ?

That is not the way fog lamps are supposed to work, at least not if they’re wired the factory way

You’re only supposed to be able to turn them on if the low beams are on

It might take an audio/accessory shop an hour to install that harness, it is rather routine. If the dark blue wire from the switch triggers the relay then the yellow wire would be connected to a low beam power wire so the fog light will only operate with the low beams on.

Depending on what decade this vehicle is from you may find that the instrument panel wiring harness does not have the wiring necessary for fog light operation, replacing wiring could cost thousands of dollars.

I’m surmising that the yellow is the power lead for the lamps. The black and white should be the trigger circuit for the relay with white being hot with the lamp switch on and the black being the ground.
A relay click sound when the black and white are touched to the battery terminals should answer that question.
The yellow should become hot when the relay energizes; IF the power source is hooked up.

This should not be difficult to sort out by a real wire guy as you refer to him. Maybe a local stereo shop could iron it out quickly. This doesn’t look like a big deal to me.

I didn’t make that suggestion. I simply asked what the OP wanted.

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Got it all hooked up $40.00 local car stereo placement. Thanks everyone.

Sounds like an elegant solution. Thanks for the update!