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Old 07-08-2010, 11:18 AM   #1
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Use factory fog light switch for aftermarket lights?


I am adding some aftermarket fog lights on my 1999 Dodge Ram. The OEM lights are past their life and I want to upgrade.

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? The Pilot kit has all the necessary components- relay, etc but I thought it might be simpler to just adapt the original plugs with a jumper to the new lights but I'm a little concerned if the extra load will be ok.

Second question is- If I use the Pilot's harness and use the OEM hot (from the dash fog light control) to power the Pilot relay I am not sure about the power circuit. One (red) OEM wire is always hot and I am not sure what the other one does. It may go through the switch to complete a ground. I just haven't had time to try to follow it and can't find a schematic online.

PS
I thought I had them working with the second method with the dash switch- turned the switch on the lights came on; turned it off the lights went off. Now the new lights wouldn't come on ( I had a loose connection) and after re-connecting that wire the lights want to stay on all the time. For some reason the original fog light connectors seem a little erratic in whether I have power there all the time or not. Test light lead was grounded at the battery and I scratched the connector contacts fairly hard several times.

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Old 07-08-2010, 02:38 PM   #2
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Use factory fog light switch for aftermarket lights?


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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Old 07-08-2010, 03:06 PM   #3
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Use factory fog light switch for aftermarket lights?


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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Old 07-08-2010, 07:38 PM   #4
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Use factory fog light switch for aftermarket lights?


Quote:
Originally Posted by downunder View Post
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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Old 07-08-2010, 09:30 PM   #5
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Use factory fog light switch for aftermarket lights?


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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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Old 07-10-2010, 09:08 AM   #6
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Use factory fog light switch for aftermarket lights?


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.

Quote:
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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Old 07-10-2010, 11:45 AM   #7
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Use factory fog light switch for aftermarket lights?


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Originally Posted by hyunelan2 View Post
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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