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  1. #1
    FEP Power Member fgross2006's Avatar
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    Default Rear Defrost mod in a convertible

    Has anyone here ever modded a vert to have stock style rear defrost?

    I found most of what I need. So far I got a heater panel with stock AC and rear defrost controls.

    I got a complete wiring harness from dash to glass from an ebay seller. I got a NOS rear defrost switch from ebay.

    Two things Im wondering about;

    first, should I replace my verts rear glass with heated glass or just ad an aftermarket heater grid on mine with a Frost Fighter setup? The interior shop that did my convertible top 2 summers ago told me $690 to replace the glass with the surrounding vinyl section. Pretty steep and not at all worth it. But then again AutoMat in Hicksville NY has always been crazy expensive. I will check one other shop then I will make a decision. Anybody have opinions on this? I did Frost Fighter 30 years ago in a 67 Camaro and I was really happy with it.

    Second, I had my mechanic print out the wiring diagram from AllData for the Defogger Circuit for an 85 LX. According to the schematic the white/purple wire gets key on 12 volts, the yellow wire goes to the starter relay and the diagram says Hot At All Times.

    I'm no electrical expert but isn't that gonna blast the defrost switch and circuit every time I start the car?

  2. #2
    FEP Power Member smitty54's Avatar
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    My question is why? Do you drive the car in the winter, or inclement weather?
    "Have you ever noticed that anybody driving slower than you is an idiot, and anyone driving faster than you is a maniac."
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  3. #3
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    The heated glass is on a relay , and a timer .
    You will also need those to finish ..
    clowns to the left of me , Jokers to the right

  4. #4
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by smitty54 View Post
    My question is why? Do you drive the car in the winter, or inclement weather?
    sometimes yes and in the summer in certain weather conditions a rear defogger is still needed in NY

  5. #5
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by ashley roachclip View Post
    The heated glass is on a relay , and a timer .
    You will also need those to finish ..

    Heres the diagram.

    It shows Yellow, Wht/PPL on one side and Gray/Yellow and black to the window grid. I assumed the time delay is in the switch. If not what part number is it? Where does it get installed? Also this diagram doesn't show any replay in the diagram. I have seen some listings for rear defog relay that's the same as the fuel pump replay. Question is how do I hard wire up the connector to the relay if I do need one?

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  6. #6
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by ashley roachclip View Post
    The heated glass is on a relay , and a timer .
    You will also need those to finish ..
    After a lot of research and getting insulted by an FEP member in another thread for asking too many questions about this stock setup I have determined that 82-86 Mustangs that came with stock rear defrost do not have a separate timer or relay or a "timer/relay". In 87-92's there is a part listing for a relay but its not applicable to any Mustangs 86 and under.

    I bought a fully complete HVAC assembly cut from an 86 still in the dash and after disassembling it piece by piece I found no relay or timer in the wiring. I decided to bench test the switch to see how it works. Grounding to the negative on a battery and running the thick yellow wire to positive I found the switch would go on but not stay on unless I held it in the ON position. I then ran the white/pink wire also to the positive terminal and now the switch stays on and runs for 10 minutes then switched itself off. I cycled 3 times with the exact same result. The switch is the timer, there no additional part.

    Its unfortunate that some douche had to insult me for asking questions which were in fact in response to Ashley Roachclip stating there are additional parts needed. All that needed to be said was "the rear defrost switch is the timer" but hey that's just me, that's how I respond to people. Others with bloated superiority issues maybe not so much.

    I appreciate your trying to help Ashley, unfortunately trying to get clarification on your advise put me in the path of a doucher.

  7. #7

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    Quote Originally Posted by fgross2006 View Post
    After a lot of research and getting insulted by an FEP member in another thread for asking too many questions about this stock setup I have determined that 82-86 Mustangs that came with stock rear defrost do not have a separate timer or relay or a "timer/relay". In 87-92's there is a part listing for a relay but its not applicable to any Mustangs 86 and under.

    I bought a fully complete HVAC assembly cut from an 86 still in the dash and after disassembling it piece by piece I found no relay or timer in the wiring. I decided to bench test the switch to see how it works. Grounding to the negative on a battery and running the thick yellow wire to positive I found the switch would go on but not stay on unless I held it in the ON position. I then ran the white/pink wire also to the positive terminal and now the switch stays on and runs for 10 minutes then switched itself off. I cycled 3 times with the exact same result. The switch is the timer, there no additional part.

    Its unfortunate that some douche had to insult me for asking questions which were in fact in response to Ashley Roachclip stating there are additional parts needed. All that needed to be said was "the rear defrost switch is the timer" but hey that's just me, that's how I respond to people. Others with bloated superiority issues maybe not so much.

    I appreciate your trying to help Ashley, unfortunately trying to get clarification on your advise put me in the path of a doucher.
    There is always going to be some butthole who thinks he knows everything about everything, don't get disheartened. I feel your pain. Just know that the work and effort you have put in here HAS answered the question for others to come. There is victory in that I think.
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  8. #8
    FEP Power Member xctasy's Avatar
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    The problem lies in the fact that often people are wrong, or that sometimes Ford changes things around. Remember just how hard its been with the VECI and EVTM (Electrical and Vacuum Trouble Shooting Manual) info really just for Ford trained service technicians. People like JACook even find it hard to be diplomatic even with this stuff. Its hard work!

    Mostly, its "we" who miss a vital clue or que, but it should never, ever stop us being the droning voice of question until we are okay to go on further.

    My sincere advice is to keep at it, and do what you do!

    Just for your info:-
    It took me 7 years to find info on a flex plate part number (I necro-ed old posts and got into a spat because of it)
    And another 13 years to get the right teeth count (I got it wrong, another member helped me out)
    I was out of pocket due to miss-information on Bolt Center spacing for Mustang wheels. (bolt Pitch Center information was ambiguous)
    I've had many, many questions over the S, V and E ports for 78 to 83 Fox Fords (info is wrong for three out of 5 years for certain kinds of Fox engines)

    For what its worth,

    I think RED 78' might have the two S and E ports around the wrong way in his copywrited over written picture material,


    and Moostsie in his description too. S is certainly the down low port on the passenger side.


    These two mistakes gave major issues with some of the Spark, BV bowel vent and EGR ports being quite wrongly positioned, and these two guys are simply excellent posters were quite wrong with the information. Nobody bats 1000.

    I've also had the same responses before, repeatedly asking the same question as many different ways I can so I can get the info I need to carry on.
    https://fordsix.com/viewtopic.php?f=...582790#p582790.

    I've decided, since I've benefited on 99.9% of JK's info being 100% right, to just suck it up and move on. But that's only because I've a history of not getting what I want, then throwing my toys out of the cot, and making it worse. You, FB, have diplomacy and better executive skills, so Keep At It.
    Last edited by xctasy; 04-14-2017 at 12:30 AM.
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  9. #9

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    Quote Originally Posted by BTD View Post
    There is always going to be some butthole who thinks he knows everything about everything, don't get disheartened.
    I am saving this so it can't be deleted. Funniest post I have seen in at least a year. I am thinking about a pot and a kettle for some reason.

    There is nothing that can't be accomplished with enough time and money invested. I am not sure who hurt your feelings fgross and frankly, it doesn't matter. This is the internet. Keep looking and I am sure someone will help you with whatever you are trying to do. I do know at one time, they made kits to install defrost in a car that did not come with it. I would imagine there is zero demand for those now so perhaps you could locate an NOS kit and use your OEM HVAC controller to control it. Sort of a hybrid of the two. Since pretty much every car and even truck now comes with it, those might be hard to come by but it is a possible source of parts for this.
    Last edited by homer302; 04-14-2017 at 08:54 AM.
    Restoration of my 84 1/2 GT Turbo T Top:
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  10. #10
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by homer302 View Post
    I am saving this so it can't be deleted. Funniest post I have seen in at least a year. I am thinking about a pot and a kettle for some reason.

    There is nothing that can't be accomplished with enough time and money invested. I am not sure who hurt your feelings fgross and frankly, it doesn't matter. This is the internet. Keep looking and I am sure someone will help you with whatever you are trying to do. I do know at one time, they made kits to install defrost in a car that did not come with it. I would imagine there is zero demand for those now so perhaps you could locate an NOS kit and use your OEM HVAC controller to control it. Sort of a hybrid of the two. Since pretty much every car and even truck now comes with it, those might be hard to come by but it is a possible source of parts for this.
    That exactly what I am planning to do. They used to have those kits in the chain auto parts stores but now they are available from the vendor online. Frost fighter is the company. The do offer complete kits or as in my case, just the rear grid to jack into the stock wiring in switch set up.

    The only thing I needed to know was is there a separate part number for a relay/Timer.

    I have all I need now to complete this mod so on to the next project.

  11. #11

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    Quote Originally Posted by fgross2006 View Post
    Heres the diagram.

    It shows Yellow, Wht/PPL on one side and Gray/Yellow and black to the window grid. I assumed the time delay is in the switch. If not what part number is it? Where does it get installed? Also this diagram doesn't show any replay in the diagram. I have seen some listings for rear defog relay that's the same as the fuel pump replay. Question is how do I hard wire up the connector to the relay if I do need one?

    Name:  Mustang Rear Defogger diagram.jpg
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    Looks like you got your answer already but to confirm......YES, the older control boxes were set up with the internal time delay and relay. No additional parts needed.

    As for the window, it's probably a ton cheaper to do an aftermarket grid than it would be to get a glass/grid combo.

    Good luck on your adventure and hopefully you can get the system to work. Rear defrost is nice every now and then, especially in a small window convertible.
    Last edited by 84StangSVT; 04-14-2017 at 10:09 AM.
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  12. #12

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    Yep, I can see how it could be useful as long as you never lower the top. However the chances of those fragile flexible metal contacts where the heavy gauge wire attaches to the window surviving a few cycles of the top are slim.
    Restoration of my 84 1/2 GT Turbo T Top:
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  13. #13
    FEP Power Member fgross2006's Avatar
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    I have couple of questions regarding rear defrost set up.

    I am almost ready to set up this mod but first can anyone tell me the route that Ford ran the hot wire that goes to the rear glass? Under the console or along the scuff plate?

    And I had to buy 2 wire sets of the same ebay seller to get all the connectors I need. One was from an 82 and the other an 86.

    The one from the 82 has a connector that splits the white/purple wire into 2. I'm thinking that the 82 setup has the amber light under the switch while the 83-86 setup has the amber light in the tip of the switch lever. Does the split power the switch and the amber LED on the 82 panel?

    I bench tested the wiring without the split and it powers up the switch for 10 minutes exactly as its supposed to. Just wanted to confirm what this 2 way split is for.

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  14. #14
    Moderator wraithracing's Avatar
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    All wiring to the back of the car would normally run down the side of the vehicles. The hatchbacks run the defroster wiring along the driver side sill plate and then to the rear driver side wheel well area where there is a ground point and multiple connections that go up to the actual hatch. These include a Defroster if equipped, the license plate lights, rear hatch release if equipped, and the 3rd brake light if equipped.

    As you stated the 83-86 have the "On" bulb in the switch lever itself and the 82 and earlier switches have an additional light although it is not an led just a small incandescent bulb. I would have to look at the control unit that came out of my 82 to verify the split in the harness.
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  15. #15
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by wraithracing View Post
    All wiring to the back of the car would normally run down the side of the vehicles. The hatchbacks run the defroster wiring along the driver side sill plate and then to the rear driver side wheel well area where there is a ground point and multiple connections that go up to the actual hatch. These include a Defroster if equipped, the license plate lights, rear hatch release if equipped, and the 3rd brake light if equipped.

    As you stated the 83-86 have the "On" bulb in the switch lever itself and the 82 and earlier switches have an additional light although it is not an led just a small incandescent bulb. I would have to look at the control unit that came out of my 82 to verify the split in the harness.

    Thanks. That's what I needed to know.

    The only thing now is the Frost Fighter kits are not as clean looking as I had hoped.

    I expected all the kits would have the tabs for power and ground at the bottom of the glass to better hide the wires but their kits have two options;

    Both tabs on the left, or one tab bottom right and one tab top left. Its dumb and it may kill my plan to do this mod. I have tried to find another aftermarket rear defrost kit and it looks like frost Fighter is the only show in town.

    Any suggestions on how to make this function and not look stupid?

    http://www.frostfighter.com/clear-vi...rosters-10.htm

  16. #16
    FEP Senior Member qikgts's Avatar
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    Have you called them with some dimensions of your window and explained what your needs are with regard to connector placement to see if they can offer up a custom configuration for you?

    To get what you want from them you might need to use their "controller" which I wouldn't rule out if it can be toggled on and off by the factory switch you have already picked up keeping the factory look.

    You may need to tell them what the amperage capacity of the switch/relay/timer combination is though.

    EDIT- FWIW, I think 94-98 SN95 cars have the two connectors on opposite sides so maybe after taking a look at one of those you could get some ideas about routing the wires.

    Edit 2- If worse comes to worse, maybe bonding some trim along the edges of the grid would allow you to run the wire(s) where you need it but still conceal it in a oem kind of way. There may be something out there that you like better but a quick google search found the link below.

    https://www.cableorganizer.com/surfa...170422063739:s
    Last edited by qikgts; 04-22-2017 at 01:41 AM.
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  17. #17
    FEP Power Member fgross2006's Avatar
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    Quote Originally Posted by qikgts View Post
    Have you called them with some dimensions of your window and explained what your needs are with regard to connector placement to see if they can offer up a custom configuration for you?

    To get what you want from them you might need to use their "controller" which I wouldn't rule out if it can be toggled on and off by the factory switch you have already picked up keeping the factory look.

    You may need to tell them what the amperage capacity of the switch/relay/timer combination is though.

    EDIT- FWIW, I think 94-98 SN95 cars have the two connectors on opposite sides so maybe after taking a look at one of those you could get some ideas about routing the wires.

    Edit 2- If worse comes to worse, maybe bonding some trim along the edges of the grid would allow you to run the wire(s) where you need it but still conceal it in a oem kind of way. There may be something out there that you like better but a quick google search found the link below.

    https://www.cableorganizer.com/surfa...170422063739:s
    I did speak to the tech at frost fighter and he said I only have 2 options. I cant imagine any car, let alone a vert, having a wire run up the glass to plug in to the top of the grid, but all or most of their kits do that.

    I couldn't use their controller with my switch because my switch has the timer built in. There'd be 2 timers in line if I tried that. The issue is the layout of their grid. The old kits used to have 2 bus bars on either side of the glass and the connectors at the bottom. I remember because I installed one in a 67 Camaro I had back in the 80's.
    Last edited by fgross2006; 04-22-2017 at 07:29 AM.

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