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  1. #1
    FEP Senior Member Purebreed1's Avatar
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    Default Under hood light

    How does the hood light get turned off when the hood shuts? I have never noticed a switch? Was this standard on all mustangs?

  2. #2

    Default Re: Under hood light

    Quote Originally Posted by Purebreed1
    How does the hood light get turned off when the hood shuts? I have never noticed a switch? Was this standard on all mustangs?
    Theres a Mercury switch built into the housing of the lamp. When the hood is up the mercury make contact with both sides of the vile completing the circuit. When the hood is down... no contact on the other side.. you get an open circuit anf the light is off.

    I have one somewhere that I took from my Edsel. I may be able to find it and post a picture. Or... you can do a google search for what it looks like.. or raid a salvage yard and have fun!
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  3. #3

    Default

    Exactly right.

    I have a NOS Mustang under hood light and harness.



    See the black module where the bulb should go. That has a mercury switch in it.

    -Mike

  4. #4
    FEP Super Member 85 Notchback's Avatar
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    Default

    .... There's a light under our hoods?
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  5. #5

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    When you have the light group ...
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  6. #6

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    Quote Originally Posted by TuxStang
    When you have the light group ...
    True.

    However, it was standard on 85-86 Capris....the light group was standardized those years. The bracket is slightly different on the Capris than the Mustangs.

    -Mike

  7. #7
    FEP Senior Member Purebreed1's Avatar
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    Default

    Those mercury switches must be prone to fail? I have never had a light work on any of the four mustangs that i have owned. I am having a rear facing hood scoop hood from a 83 put on the car and would like to get a working light for it. I never checked the one that is on there but I am going to assume it is no good.

  8. #8

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    Quote Originally Posted by Purebreed1
    Those mercury switches must be prone to fail? I have never had a light work on any of the four mustangs that i have owned. I am having a rear facing hood scoop hood from a 83 put on the car and would like to get a working light for it. I never checked the one that is on there but I am going to assume it is no good.
    Mercury switches generally don't fail.

    These lights stop working because:

    1. Blown Bulb. Most owners don't bother replacing them.
    2. Rust/Corrosion takes its toll on the bulb and wire connections. These things seem to always be rusted badly.
    3. Busted wire (very very common) either from normal use or getting cut from a hood swap or just because somebody is too lazy to figure out the real problem and wants the wire out of the way.
    4. The in-line fuse is blown.
    5. Bad ground to the hood.

    I tested an old rusted/coroded one that I used some rust converter to get rid of the rust and cleaned it all up and it still tested aok.

    -Mike

  9. #9

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    ^ Exactly.

    On my LX... somebody had cut the wire off at about 2" or so from the socket. The socket was also located on the passengers side just above where the upper radiator hoae is (dumb place IMO). I was getting a weird deformed hose after I upgraded to the larger Alternator and couldn't figure out WHY I was getting it. Then it dawned on me why. No more deformed upper hose.

    The one in my Mustang has a bad socket... not the mercury switches problem... but a spring problem (or so it seems for now). I've not bothered to fix it. It's not one of my top things on my "important things to do" on my car repair list.
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  10. #10
    Travis T
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    Default

    Quote Originally Posted by TuxStang
    When you have the light group ...
    My 84 GT does not have the light group, and it has an underhood light. Possibly standard on the GTs?

  11. #11
    FEP Power Member StangBoy's Avatar
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    Default

    Quote Originally Posted by Travis T
    Quote Originally Posted by TuxStang
    When you have the light group ...
    My 84 GT does not have the light group, and it has an underhood light. Possibly standard on the GTs?
    i believe so as gt's had the light goup.
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  12. #12

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    The "light group" was optional. It was not standard with the GT model.

    My '83 GT has neither the light group nor the underhood light.
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  13. #13
    FEP Senior Member Purebreed1's Avatar
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    Default

    That is good informattion. I will take a look at the socket and start tracing it from there.

  14. #14
    FEP Power Member fgross2006's Avatar
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    Default

    Quote Originally Posted by negusm View Post
    Exactly right.

    I have a NOS Mustang under hood light and harness.





    See the black module where the bulb should go. That has a mercury switch in it.

    -Mike

    Was there an option for a hood light for 84?

    I was thinking of customizing a setup with a hood light for 89 to 04 since they are common. But I stumbled on this thread and saw the part for 86 to 86. That part is hard to find these days.

  15. #15

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    Quote Originally Posted by fgross2006 View Post
    Was there an option for a hood light for 84?
    Yes. My 84 GT has it. I have removed it as I don't use it though.

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    Last edited by 84StangSVT; 03-20-2017 at 06:46 AM.
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  16. #16

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    Light Group was optional in all Mustangs except SVO through 1986. It was standard in 1984-86 SVO and in 1987+ Mustang.
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  17. #17

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    Quote Originally Posted by fgross2006 View Post
    Was there an option for a hood light for 84?

    I was thinking of customizing a setup with a hood light for 89 to 04 since they are common. But I stumbled on this thread and saw the part for 86 to 86. That part is hard to find these days.
    Its on my 84 GT, but I have the light group. Mine works, but I have it unhooked so when I'm working under hood it doesn't drain the battery.
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  18. #18
    FEP Super Member sowaxeman's Avatar
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    Default

    Quote Originally Posted by vxr500 View Post
    Its on my 84 GT, but I have the light group. Mine works, but I have it unhooked so when I'm working under hood it doesn't drain the battery.
    Many people do this for shows when the hood is up. But for common safety sake, you should be unhooking the "-" on your battery before working under the hood

    The negative is never hooked up on my cars accept for when I am driving them. Can never be too cautious with these old carb'd cars that had their known fire issues back in the day.
    Last edited by sowaxeman; 03-20-2017 at 10:23 AM.
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  19. #19

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    Quote Originally Posted by sowaxeman View Post
    Many people do this for shows when the hood is up. But for common safety sake, you should be unhooking the "-" on your battery before working under the hood

    The negative is never hooked up on my cars accept for when I am driving them. Can never be too cautious with these old carb'd cars that had their known fire issues back in the day.
    point taken
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  20. #20
    FEP Power Member fgross2006's Avatar
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    I did some searching on ebay last night. One guy is selling a light listed for 86 and he wants $125, part number E5ZZ-15702-A
    http://www.ebay.com/itm/Ford-OEM-Und...3D381814121814

    This one is listed roe an 84 Topaz, part number E43Z-15702-B
    http://www.ebay.com/itm/391702512619...%3AMEBIDX%3AIT

    This one is listed for 86 to 89 Econolines, part number E6UZ-15702-A
    http://www.ebay.com/itm/381814121814...%3AMEBIDX%3AIT

    Visually these all look the same and the 15702 is common in all these parts. In my haste to get a stock looking light without spending 125 bucks I grabbed the one for the E-150-350. I found the parts for 84 Topaz pretty abundant on ebay and Im sorry I didn't take one of the those. Is there any real difference in these 3 parts and respective parts numbers? Im thinking the Econoline hood opens nearly 90 degrees so maybe the mercury in the switch is set at a different angle to illuminate? If so I can still get one of the others.

    I assume the ring terminal in the wiring goes to the positive side of the starter relay?

  21. #21

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    Quote Originally Posted by fgross2006 View Post
    I did some searching on ebay last night. One guy is selling a light listed for 86 and he wants $125, part number E5ZZ-15702-A
    http://www.ebay.com/itm/Ford-OEM-Und...3D381814121814

    This one is listed roe an 84 Topaz, part number E43Z-15702-B
    http://www.ebay.com/itm/391702512619...%3AMEBIDX%3AIT

    This one is listed for 86 to 89 Econolines, part number E6UZ-15702-A
    http://www.ebay.com/itm/381814121814...%3AMEBIDX%3AIT

    Visually these all look the same and the 15702 is common in all these parts. In my haste to get a stock looking light without spending 125 bucks I grabbed the one for the E-150-350. I found the parts for 84 Topaz pretty abundant on ebay and Im sorry I didn't take one of the those. Is there any real difference in these 3 parts and respective parts numbers? Im thinking the Econoline hood opens nearly 90 degrees so maybe the mercury in the switch is set at a different angle to illuminate? If so I can still get one of the others.

    I assume the ring terminal in the wiring goes to the positive side of the starter relay?
    You are correct on the hook up point. It goes to the infeed + side of the starter relay. As for the angle of how much the hood opens, I have never seen a mercury style switch that really was set different. It's a pretty simple system and as long as the switch is off level it should function. Any degree of bulb higher than base should illuminate the bulb and any degree of bulb lower than base should shut it off. Most of the time, the only difference to make up for the angle of the hood is in the bracket that the bulb/base mount onto. Worst case scenario is you will have to tweak the mounting bracket a bit to get the best function.

    Hope this helps.
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  22. #22
    FEP Power Member fgross2006's Avatar
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    Default

    Quote Originally Posted by 84StangSVT View Post
    You are correct on the hook up point. It goes to the infeed + side of the starter relay. As for the angle of how much the hood opens, I have never seen a mercury style switch that really was set different. It's a pretty simple system and as long as the switch is off level it should function. Any degree of bulb higher than base should illuminate the bulb and any degree of bulb lower than base should shut it off. Most of the time, the only difference to make up for the angle of the hood is in the bracket that the bulb/base mount onto. Worst case scenario is you will have to tweak the mounting bracket a bit to get the best function.

    Hope this helps.
    Sounds logical, but I noticed the mounting bracket for the E150-350 part is flat and the ones for the Escort/Mustang are at an angle. That would affect position of the bulb and mercury switch. Im gonna grab one for a Escort, only 22 bucks. One of them has to work.

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