# Use factory fog light switch for aftermarket lights?



## Mr Chips (Mar 23, 2008)

i would use the wiring and relay the kit came with just so i could use them with headlights out, or even highbeams if i wanted. most OEM fogs only work when headlights are on, and will go out when highbeams go on. 

As far as if your higher wattage lights can be used with OEM switch, it's really impossible to answer correctly without knowing what the OEM wiring gauge is. Does your OEM switch go through a relay? If so, you should be good, if not you'll need to see that the wire guage is and see if it can handle the extra load needed for the big wattage jump


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## hyunelan2 (Aug 14, 2007)

For ease of wiring, I would personally cut the connectors off of the OEM fog harness, and splice in the line to the new fog lights and call it a day. The OEM harness wires will already be through relays and everything they need to be.

If you want to use the new relay and wiring, you could use the existing fog light line to be the trigger for the relay - thus retaining the OEM switch. 


P.S. In the U.S. it is illegal for fog lights to be on with high beams (USDOT Code)- that's why they shut off OEM when you turn on the high beams. Also, if you are using your high beams to see distance, you typically do not want the area right in front of you lit up (fog lights). It's like trying to look out your house window at night with the lights on in the house, vs. shutting them off. If the lights you purchased are not truly "fog" lights and are instead "Driving lights," then it's like using a second set of high beams and you may want to override the OEM circuit.

P.P.S. if you live in a state that requires vehicle safety inspections, if your fog lights do not turn off when the high beams turn on - you will fail inspection.


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## Yoyizit (Jul 11, 2008)

downunder said:


> I have Pilots with 55 watt bulbs. The OEM lights have the 37.5 watt bulbs. Any problem with using the OEM wiring with the little bit of extra current?


I'd be more concerned with the original switch contacts failing under the heavier current.


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## hyunelan2 (Aug 14, 2007)

Yoyizit said:


> I'd be more concerned with the original switch contacts failing under the heavier current.


In a modern automobile, the current for the lights is not going to flow through the switch. The switch only carries enough load to be a trigger for a relay. You might have to worry about the relay being able to handle the bigger load, but I would imagine that an OEM relay installed for 75w could carry 110w. Worst case scenario is a blown $2 relay.


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## downunder (Jun 13, 2008)

*Update*

Most important finding-Learned that the dash switch controls the ground circuit. I haven't done this kind of wiring since the 80's. Things have changed! All higher current +wires stays under the hood and is handled via relays. Dash switch only contols ~0.3 amps. This will not change irregardless what other lights I add. It only closes the ground that activates the relay under the hood.



> If you want to use the new relay and wiring, you could use the existing fog light line to be the trigger for the relay - thus retaining the OEM switch.


That was my original thinking based on my (outdated) experiences from 20-30 years ago.

Found some schematics and ground wire ID. Went into the PDC box and tapped the ground wire from the 85 relay terminal.

Connected the _on/off switch to relay wire_ to the battery for power to operate the relay EM.

I used everything that came with the light kit except the on/off switch, including the relay as noted in original post.

I now have aftermarket lights that operate from the dash switch exactly the same as the original lights did.

hyunelan2
After I eventually found some schematics, your wiring information was right on the money.
PS- At the risk of sounding a little negative, I bought fog lights to replace fog lights to use when I am driving in the dark in rain/fog. I know the difference between fog lights and driving lights. And I have 25 years background in law enforcement. I know what the law says about the operation of fog lights, driving lights, etc. and I had no problem whatsoever about writing tickets to @#$holes who blinded me when I was on duty.


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## Yoyizit (Jul 11, 2008)

hyunelan2 said:


> an OEM relay installed for 75w could carry 110w. Worst case scenario is a blown $2 relay.


You're right. I forgot that there is more than one fog light.

I'd stay with skinny wire to prolong bulb life.


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