1. #1
    Jozjep's Avatar
    Jozjep is offline Junior Member
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    Factory Fog light issue!

    Hey guys, I have an 04' TJL with factory bumper mounted fog lights. They have not worked since I purchased the Jeep. I have replaced the bulbs and relay so far but still no fogs! I am not an electrical guy so I have not used a meter at all but in my mind the only thing left is to replace the switch. I figured I would post first to see if I am missing anything before dropping another 60 bucks on this issue.

    Thank you in advance,

    Joe

  2. #2
    greg92jeepxj's Avatar
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    Re: Factory Fog light issue!

    Before resorting to purchasing new fog lights , you must find why the lights aren't working . The only reason you would replace the lights would be if they were corroded and no amount of repair would be of help. Understanding that your not very experienced in electrical shouldn't bar you from trying to diagnose the problem yourself. I'll try to explain some very simple and basic tests involving a test light or meter . Be advised that some advanced electrical necessitates a wiring diagram since you'll want to be sure the circuit isn't powered or feeding back to the body control module or powertrain control module . Circuits that do need to be handled with computer safe equipment . The safest way is to obtain a computer safe test light . That way , you'll be assured that any circuit you check will be drawing only a minimal draw and will not cause an over draw causing damage to a circuit and/or the BCM or PCM . I don't wish to intimidate or even scare you from performing this diagnostics yourself but only want to advise you of the proper way and not cause any harm to your vehicle. Fore warned is fore armed .
    The computer safe test light only draws about a quarter of a volt to power its diode type light bulb just as led lights do and don't tax the electrical system as some higher amperage lights do. A good multimeter that is computer safe with a ten mega ohm impediance rating is safe for this work but I don't think you'll need such an advanced / expensive meter to diagnose this problem . But at the same time , I wouldn't want you to get one of those cheap/ free multimeters such as harbor freight sells and put your jeep at risk and add to the problem . You would be surprised how many times someone starts out simple such as a light problem and "spiked" a computer circuit . I too once caused such an overdraw on a computer circuit because I didn't use a computer safe test light . the good thing about these test lights is that they can differentiate between positive and negative polarity just as a good multimeter can to let you know that you've made an incorrect connection and mistaken a loaded circuit for a ground. That is why it's best to use a computer safe test light. To check a loaded circuit ( one that is live) , attach the lead ( usually an alligator clip) to a ground and probe ( touch ) the suspected wire or terminal that carries power. If you were sure you know which wire or terminal is the live side and which is the ground ( via a wiring diagram ) , you use the alligator terminal on a body ground to check for a live circuit . Conversely , you would connect the alligator clip to battery positive and probe the ground . The computer safe light will glow red when probing a live circuit and green when probing a ground circuit. It is important to check both circuits since it does no good for a light socket for instance to receive power if the ground side isn't carrying back to the battery negative thereby not completing a circuit. Start at the light socket itself with the switch on and ignition on as well since it's likely the circuit is ignition fed and only live when ignition is on . A word about test lights ; nothing is foolproof so it's best to have a wiring diagram to be certain which wire feeds and which wire grounds . Color codes can be misleading on different make , model & year . I never chance crossing a circuit . It's always best to use the light with the alligator clip to ground since no harm can be caused by grounding a ground circuit . Grounding a live circuit with a computer safe light will just light up the diode on the test light and will be red. Only attach the alligator lead to battery positive to check a ground if your sure the circuit will be a ground. If you do not find power and are not sure which wire or terminal should be power or ground , it's time to check the switch . You'll want to check for power and from what terminal when the switch is on . If none is found , time to check fuses and / or relays marked for the fog lights. Probe both sides of fuse terminals for power and terminal 30 of a relay for power . Terminal 30 feeds terminal 87 which feeds the source I.E. , a fog light. Terminal 87 won't be live until a switch is turned on to power terminal 85 which carries through terminal 86 ( ground or continuous feed to another relay ) . This sounds daunting but keep it simple at first by looking for power continuity ( the ability of volts to flow through a circuit ) to the light socket then at the switch. Look for any fuses and relays marked for fog or auxiliary lights. I am by no means an experienced electrician but the knowledge I've learned may be helpful to you and hopefully to anyone who should experience this or another similar problem . There are regular test lights which aren't computer safe but they can only be used on a circuit that is a known non-computer and low amp circuit. Alternator and starter circuits need high amp test equipment. Hope this helps . Your welcome to post back your findings and post any questions .
    Last edited by greg92jeepxj; 08-07-2016 at 11:57 AM. Reason: Typo and errors
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    Re: Factory Fog light issue!

    Something I forgot to mention is that if it becomes necessary to test a wire for continuity , it must be done when the circuit is unloaded . That means NO electricity is flowing through the wire AT ALL . Disconnecting the wire at both ends is the surest way and will assure you that your testing only the wire and not any connection . An ohm meter will be necessary . That cheap multimeter I mentioned in my last post can do this AS LONG AS the circuit is unloaded . Keep track of what color wires run from the fog light wiring back to the switch to match them . You can now attach the test leads from the meter set to ohms to confirm continuity . As long as the wiring from the light(s) can flow electricity to and from , that should rule out a problem there . But don't over look a good connection with the bulb itself . If the ohm meter can read voltage from its own battery through the feed wire and return ( ground) then the circuit is complete . That is when it needs to be confirmed that the switch is working right and actually receiving voltage to feed the lights. Socket contacts can be notorious for this . Blown bulbs are second to that . If a wire can be pulled in and out of a socket , the terminal contact is most likely NOT making good contact with the bulb .
    Last edited by greg92jeepxj; 08-07-2016 at 12:18 PM. Reason: Additions
    Never overlook the obvious . It's usually right in front of us

  4. #4
    JPNinPA's Avatar
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    The multi function switch does go bad. It's a known issue with Tj models. Not saying that is the issue but a simple voltage check will confirm.
    Start at the lights work back to the relay and switch... Be sue the fuse is good. Check and clean the grounds, if anything poor grounds are the source of many issues.


    If you have the $$ and time wire your fog, headlights and high beams so they have separate relays that do not go through the multifunction switch. Many clams to get more lumens or brightness from their lights.
    "Never look down on anybody unless you're helping him up" - Jesse Jackson

  5. #5
    Jozjep's Avatar
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    Re: Factory Fog light issue!

    Wow thanks guys! I will try and mess with it and report back this weekend.

    Joe

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    Re: Factory Fog light issue!

    I have a 2006 TJ. There are currently not any fog lights however the wiring harness is in place in the front fenders. If I wanted to add fog lights utilizing the stock harness, what would be the best way to control them (The current Multi-function switch doesn't have fog light control). Since the harness is in place, If I replaced the multi-function switch with 1 that had fog light control, would that be all that is necessary or would i have to add a relay also?

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    JPNinPA's Avatar
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    Factory Fog light issue!

    Honestly wire them to a relay off the battery and to a control switch. This way you are not dropping voltage through the switch. The lights will be brighter and the switch will last longer than the stock switch.
    KChilite has good wiring diagrams.


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    "Never look down on anybody unless you're helping him up" - Jesse Jackson

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