[KB] Turning fog lights on indepent of headlights

[northwichita]

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Copied from another page, if anyone could point to something simpler feel free to.



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I finally got around to rewiring the Fog lights on my 06 pkg 6. Since I Have HID's, standard 1/2 voltage DRL's arent' possible. It took a bit of work and it isnt for the faint of heart but works like a charm. Now to upgrade the bulbs themselves.

First, the Fog Light relay under the hood (long relay box in center of engine compartment) only has power when the park lights are on. Starting here, unbolt the 2 10mm bolts and flip the box over, remove the cover and you will see the back of the relays. Locate the Fog lamp relay (2nd from left) and cut the BROWN wire a few inches away. You will now connect this to the PURPLE of the PTC HTR 2 relay next to the fog relay. This is an IGNITION - ON feed and allows the relay to be triggered only when the Igntion is ON. Put everything back together. Now the relay can only operate when the car is ON - instead of only when the lights are on.

Next pop the bottom cover off of the steering column and access the flasher/lights plug( See knowledge base info under EV switch for details) Find the ORANGE wire (fog light switch ground - provided by low beam switch)...cut it and jump the switch side to the DARK GREEN wire in the same harness(low beam switch ground). Tape off the other cut ORANGE wire end and your done here. Put the column back together. You have now allowed the FOG switch to use a CONSTANT ground signal, unaffected by the headlight switch.

THis is the hard part, following other instructions on the site, You can either follow the directions for accessing the 2 wires given in the Knowledge BAse article about making the Fog Lights work indepndant of low beams or do it my way(easier on the back smile.gif . Drop the lower dash panel, remove the 3 10mm nuts securing the metal plate, and then the 3 10mm bolts securing the fusebox/body ECM to the dash (top 2 bolts are machine thread, left bolt is a coarse thread into plastic). Release and unplug all of the plugs on the FRONT (side facing the driver's seat) of the fuse box. MAKE SURE THE CAR IS OFF before doing this. (this will erase the clock and MPG memory).

At this point, it will be easy to rotate the fuse box around and see the Body ECU plugs on the back top. 3 plugs. You want to unplug the one closest to the drivers side.

Locate the YELLOW and Lt. BLUE wires in pins 13 & 17 (they are caddy -corner to each other). Cut them off and connect the car sides of the wires to each other. Tape off the ECU sides and put everything back together. You have now just bypassed the Body ECU's ability to regulate Fog light usage.

So, now, when you turn the Fog light switch ON, you provide a direct ground to the Fog Light Relay under the hood which receives it power now from Ignition. The Fog lights can now be left on and will come on when the vehicle is started. They are totally unaffected by head/park light usege.

Took me about an hour but add a few hours for those not as familiar with electrical work.


--------------------
Scott West
Auto Security, Video, Audio, Nav Installer - 16+ yrs
MECP Certified
San Bernardino, CA

[satwood]

Scott,

Why do you need to bypass the ECU control of the fog lamps? What does the ECU do to control their usage? If I simply did the first two mods bu didn't do the third, what would be the result?

Thanks
Steve

[SDBobcat]

Call me a Geek if you like, but... In some states (Ohio for one, at least before I moved to Cali 10 yrs ago) it is illegal to drive with just runing or fog lights. At least that the reason the officer gave for pulling me over.

[Steamboatsig]

Originally Posted by SDBobcat

Call me a Geek if you like, but... In some states (Ohio for one, at least before I moved to Cali 10 yrs ago) it is illegal to drive with just runing or fog lights. At least that the reason the officer gave for pulling me over.

Geek!

There are some instances like heavy snow or fog where the HID's make it impossible to see. The only solution would be to run the fogs only. Yes, there are states that do not allow you to drive with your fogs only, but I would think any reasonable officer would understand you using fogs only if there was heavy snow or fog.

The other situation would be allowing the use of fogs with the highbeams. I remember someone saying that most states do not allow more than 4 lights pointing forward on at a time. That is why most fog lights turn off when you switch to highbeams. The arguement can be made that no additional lights come on when the Prius switches to highbeams, it simply moves a reflector.

[NoMoShocks]

Originally Posted by satwood

Scott,

Why do you need to bypass the ECU control of the fog lamps? What does the ECU do to control their usage? If I simply did the first two mods bu didn't do the third, what would be the result?

Thanks
Steve

I see that this question was never answered. The result would be that the fog lights would still only work if the headlights were on, in High Beam as well as Low Beam. I have been studying the wireing diagram and Service Manual for the Lighting system. The ECU is included in the Fog Light Switch circuit to operate the Fog Lights only if the Head Lights are on. Although the other terminal of the Fog Light relay coil is connected to the Tail Light circuit, the Tail Light come on if just the Parking Lights are on, so the additional ECU control is needed.

I am not sure why the +12 V end of the Fog Light relay is connected to the Tail Light circuit. Maybe the desinger just found that to be a conveniently located adacent power source.

I have attached a wiring diagram showing the electical connections for the three modifications. I will try this tomorrow and report back on how it works out for me.
Fog Light Mod.pdf

[ilusnforc]

Reviving an old and dead thread... Does this mod provide any different function than what is described on Darell's site? Or does it work exactly the same way?

Fog lights

[auricchio]

It's amusing...I came up with a similar mod.

Rather than hacking into the dash, I just added a convenient ground for the fog relay. A short jumper to the relay-box mounting bolt.

Instead of cutting wires inside the relay box, I just pulled the fog relay and let it "float" on the new wires. Completely reversible, no need to pull the relay box, no work under the dash.

I'm content to go with full-time fogs till I get pulled over for a fix-it ticket.

NoMo, using the taillight 12v was convenient because that's only active when the parking/headlights are on. It probably simplified switching in the combo light stalk switch.

Edit: Here's the link: Cheap Fog-DRL Mod

[satwood]

Why is this mod considered illegal in the US? I've seen several references to it being a questionable thing. I can understand driving without your headlights on at night, but why is having fog lights on during the day wrong?

[qbee42]

Originally Posted by satwood

Why is this mod considered illegal in the US? I've seen several references to it being a questionable thing. I can understand driving without your headlights on at night, but why is having fog lights on during the day wrong?

I comes from people using too many forward lights, blinding oncoming traffic. You can make a good argument that the stock fog lights are so dim that they couldn't possibly blind anyone, but laws are written for the general case.

If allowed, some drivers will load up their trucks, SUVs, and performance cars with banks of bright lights. That is why many states restrict automobiles to no more than four headlamps, and only two during good weather. The exception for bad weather is because of the need for additional illumination.

Tom