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  1. #1
    FEP Senior Member tbirdman's Avatar
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    Default Fog Light Success...Well...Partially

    So buoyed by my discussions at the beginning of the year with one of the members here (michaeloberg1980) and his success with getting his fog lights working, I decided to tackle my fog light issues. Today I went about seeing if I could get them fixed. First I took a piece of 16 gauge wire and soldered a 20 gauge repair fusible link section to it...

    Name:  20ga. Fusible Link.jpg
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    I attached the looped end of the fusible link to the hot terminal on the starter relay and ran the wire into the passenger compartment. After getting it inside, I checked the wire and found that I was getting 12v at the end of the wire. Yeah! I disconnected the connector from the relay and found that there was no power at the end of the factory power wire coming into the relay, so I figured I was on the right track. I crimped on a female connector to the end of my replacement wire and installed that into the relay connector where the original wire had been. I replaced the connector onto the relay and gave it a go. No fog lights. I replaced the aftermarket relay with a factory relay that I had, and still no fog lights. I disconnected the 2 pin connector from the back of the fog light switch and inserted a jumper wire into the female ends of the connector, still no fog lights...but the fog light power light came on (for the first time), so again, figured I might be on the right track. I disconnected the passenger side fog light from it's connector and checked for power at the connector. I did have 12v at the connector. So why didn't I have power at the light? I cut two short sections of wire and ran it straight from the battery into the connector on the fog light. Viola...power! I cleaned up the pins on the connector, applied a bit of dielectric grease, reconnected, and for the first time in 13 years, had a working fog light.

    The second fog light was not as simple. That one would not come on using the power straight from the battery. Turns out it had a bad bulb holder. Luckily I had a replacement fog light in my parts stockpile in the basement and was able to confirm that it worked. I installed it and now had two working fog lights. Woohoo!

    I also had a spare fog light switch. I installed the two pin connector onto the back of tho spare switch, but couldn't get the fog lights to come on with that switch either.

    So...that brings me to a question... I know it's possible, however unlikely, to have two bad fog light switches. Since I was able to jumper the connector and get power, I'm assuming that the switches must be bad, since all they do is complete a connection. When I checked the second fog light switch for continuity, I wasn't able to come up with anything, either with the switch on or off. I was only checking continuity between the two pins at the back of the switch. I saw the two leads that go to the power illumination bulb, but I'm thinking that, based on the wiring diagrams that I have and the fact that the power light came on when I jumped the pins, they appear to be on a separate circuit?

    Am I checking the fog light switch correctly?
    Last edited by tbirdman; 04-19-2020 at 09:52 PM.
    If they take my stapler, then I'll set the building on fire...

    85 Mustang GT

  2. #2
    FEP Super Member gr79's Avatar
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    Default

    http://www.mustangandfords.com/how-t...ight-switches/
    https://books.google.com/books?id=pL...-17-11&f=false

    Multifunction switch E8ZZ-13K359
    Connector E6DZ-14489-P
    Headlight switch E7ZZ-1154-B
    two terminals D8TZ-1474-A
    Circuit number 15's yellow striped red wire with length of 12g cable.

    Ford TSB 89-17-11 has details.

    From page 165 Mustang 5.0 Tech Ref and Perf. Handbook
    Foglight difficulties:
    "An intermediate non-factory approach calls for replacement of too small production cable with higher capy wiring and thorough cleaning corrosion from all connectors and terminals. "

    Had intermittent foglite. Have Bosch. Was ground in bulb holder.

  3. #3

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    Quote Originally Posted by gr79 View Post
    http://www.mustangandfords.com/how-t...ight-switches/
    https://books.google.com/books?id=pL...-17-11&f=false

    Multifunction switch E8ZZ-13K359
    Connector E6DZ-14489-P
    Headlight switch E7ZZ-1154-B
    two terminals D8TZ-1474-A
    Circuit number 15's yellow striped red wire with length of 12g cable.

    Ford TSB 89-17-11 has details.

    From page 165 Mustang 5.0 Tech Ref and Perf. Handbook
    Foglight difficulties:
    "An intermediate non-factory approach calls for replacement of too small production cable with higher capy wiring and thorough cleaning corrosion from all connectors and terminals. "

    Had intermittent foglite. Have Bosch. Was ground in bulb holder.
    great info! Thanks for posting!
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  4. #4
    Moderator wraithracing's Avatar
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    Not sure exactly what year model vehicle is being repaired,but an FYI the headlight and multi function switches linked to above are for the 87+ Mustangs and not any 79-86 Mustangs/Capris.
    ​Trey

    "I Don't build it hoping for your approval! I built it because it meets mine!"

    "I've spent most of my money on Mustangs, racing, and women... the rest I just wasted."

    Mustangs Past: Too many to remember!
    Current Mustangs:
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  5. #5
    FEP Senior Member tbirdman's Avatar
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    I've seen the info on running new wiring for the fog lights, both on this website and on other Mustang websites. I would like to keep it as close to stock as possible, that's why I wanted to use the original fog light switch. I spent some time getting wiring out of the car that someone had ran for an alarm. I don't really want to add additional wiring/relays that aren't supposed to be there. This ended up only being one additional wire.

    I was pretty sure my main problem was with the main power feed coming off the fusible link in the engine compartment, which is why I ran the replacement wire. This is only a temporary thing (ha, how many times do we say that!). Eventually I will work on repairing the harness which has the fusible link in it. I also just secured an engine, dash and main harness from an 85 GT that I am going to use to try and research where the repair needs to be made.

    So my question then is still about the fog light switch. Shouldn't I be seeing continuity when the switch on the fog light is in the "on" position and the leads are connected to the two pins at the back of the switch?

    This work was done on an 85 GT.
    If they take my stapler, then I'll set the building on fire...

    85 Mustang GT

  6. #6
    FEP Senior Member tbirdman's Avatar
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    I think I may have got it worked out. I cleaned off the two pins at the back of the second fog light switch and then did the continuity test, and discovered that I did have it. I'm going to buy some electrical contact cleaner and see if that cleans up the pins better. Then will try the switch over the weekend in the car to see if that fixes it.
    If they take my stapler, then I'll set the building on fire...

    85 Mustang GT

  7. #7
    FEP Senior Member tbirdman's Avatar
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    Finally got it finished. I was able to clean up the backup fog light switch and get that working. It was a pain getting the existing fog light switch in the car out, but I got it replaced.
    If they take my stapler, then I'll set the building on fire...

    85 Mustang GT

  8. #8
    FEP Senior Member OX1's Avatar
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    Quote Originally Posted by tbirdman View Post
    Finally got it finished. I was able to clean up the backup fog light switch and get that working. It was a pain getting the existing fog light switch in the car out, but I got it replaced.
    Good deal, does it have the little orange LED and does that work?
    86 Capri, 5.0, 5Spd, A9L QH/BE, 47 lb Inj PMAS 3" MAF, Single T44 Turbo, Front Mount IC, TW170,
    Stock Cam, Explr Intake/TB, 1.7 Rockers, CF dual friction clutch, 3" DP, 2.5" full Exh, 3.27, 11.932 @ 115.78
    84 LTD, 331-10:1, TW170/Exprl Intake, 47 lbs inj/80 mm LMAF, Full Duals, Quarterhorse, Vortech 7PSI, Lentech AOD, 5 lug Mk VII brakes/rear, Eibach Sway bars, Cobra HB (dads ride, but I fix it )

  9. #9
    FEP Senior Member tbirdman's Avatar
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    Yes, it has the orange indicator and that does work too.
    If they take my stapler, then I'll set the building on fire...

    85 Mustang GT

  10. #10

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    Congrats!

    Its a great feeling getting the fogs working. My 86 GT didn't have them for twelve years. I started at the bulbs and worked my way back towards the switch and then to the fusible link like the EVTM lists. Turns out the relay was bad and tracked one down and bingo. I also needed a new bulb and lens to boot. Not sure about the 85s but on the 86s there is a connection with the O2 circuits- if I recall the fusible link protects both fogs and O2s. Nothing like being an automotive Indiana Jones- especially when it pays off. 80s cars look great with the square headlights on plus the fogs below.

    Cheers!

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