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4ZUA787
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Discussion Starter · #1 ·
has anyone ever installed a rear deforter into a gt befor. i have found several places that i can get the rear defroster winshield from but have no idea were to get the electronics for it or if all defroster systems are the same and could just steel a unit from a bimmer or any other car. help???
 

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You can buy defroster grids that stick on, and they come with hardware, etc. The other option would be to buy one of thoes small 12V space heaters, and mount it on the back deck. I'd choose option one.
 

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GT heated backglass

This was a factory option on Opel GT-ALs, I'm not certain if the GT/J models offered it. The GTs with this option were equipped with a 35 amp alternator (during the years when the Bosch 28 amp alt was standard, pre 1972), a blue indicator light just below the left dash vent, the heating grid and associated wiring, and a special external-fuse relay, located down by the headlight relays. ALL US-spec GTs have the switch on the dash--it's between the wiper switch and the fan motor switch. Look closely, it's THERE. BTW, anyone with one of these heated backglass relays to sell, let me know . . . will pay cash, trade, whatever.
 

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4ZUA787
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Discussion Starter · #4 ·
defroster

yah i have looked at opels unl ogts and opelgtparts.com
ogts doesnt have any parts for the rear defroster
opels unl sells the rear defroter window as does opeljunkyard.com
and on the opelgtparts.com site they sell the little light assembly for the defroster so really i have every thing but the brain available to me. well ill try and find a place that has the brain unit.
well till then im on a search.
 

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No sweat. Most Auto supply stores sell the stick-on defroster grid, and you just need a 12 volt relay, supplied by the main fuse box and activated by the factory switch. As I recall, the factory wiring setup had the relay switch power coming off the alternator (and regulator) D+ so that the defroster would only be "powered" when the engine was running.

When I installed my first grid defroster (years ago), I had trouble getting the grid lines parallel and level. I have since learned two tricks. Place rows of tape on the OUTSIDE of the window as a pattern to follow. And if possible, remove the rear window to make it easier to install the grid wires; there isn't much room between the parcel shelf and the window otherwise, but it can be done.
 

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Why that particular relay?

In all honesty, the only thing special about the defroster relay is the built-in fuse holder. If you are willing to use an in-line fuse holder, any standard 30A fog-lamp style relay should work the same if wired-up as follows:

-Most relays, horn ones being the exception, have either 4 or 5 terminals on them. Traditionally they are labeled 85, 86, 87 (one or two 87's), and one labeled either 15 or 30. The auto industry, or at least the European auto industry, standardized the circuit designaters for almost all cars in the 50's, so a 30 is almost always a battery (+), a 15 is a (+) when the ignition switch is on, a 50 is the (+) for the starter, and so forth regardless of whether you are talking about an Opel, Audi, Citroen, or whatever. Those designators stuck and are still being used today. This is all by way of explaining that you can buy a $4 relay and wire it in using the designators in the Opel wiring diagram and the markings on the side of the relay and it will work fine.

-Terminals 86 and 85 are for powering the coil in the relay. Direction of current doesn't matter between the two, so they are completely interchangeable electrically as long as between them is 12V when you want to energize the relay. Typically they are wired-up so the one is grounded near the relay and the other gets power from the ignition through a remote switch, but the Opel defroster is wired differently. In the Opel, the (+)12V comes from the output of the alternator via the same wire the idiot light on the dash uses.
(If the alternator is not working this wire has 0V, the idiot light will use it as a ground to light-up, and there will be no power to energize the defroster relay. When the alternator is working, there is 12V on this wire, supplying the power to energize the relay and keeping the idiot light turned off. This is how Opel kept you from draining your battery too quickly with the defroster on.)
The other lead on the relay will ground to the chassis through the switch on the dash, completing the coil circuit only when the switch is shut and the alternator is putting out power. The switch in the dash already has one side hooked-up to ground and the light on the dash should already be wired-up as well so if the wire above is connected to the empty terminal 86 on the back of you switch cluster you shouldn't have to do anything else for the control circuit.

-Terminal 30 (sometimes 15) is for power from the battery. The best connection is probably a big lug on the big post on the starter. This line is the one that will need a fuse installed. I recommend 16ga wire at a minimum for this and the wire to the defroster.

-Terminal 87 is the terminal that will now see 12V when the relay gets energized. Route a wire and hook this up to one side of the defroster grid. The other side of the grid hooks up to ground, typically a screw into the sheetmetal support around the window or below the rear shelf.

You should be able to see all the wiring in the wiring diagram you can download from OANA. Just add in the wires to replace the dashed lines on the diagram with wire and hook-up a cheap relay acording to it's own terminal labels and you should be set!
 

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4ZUA787
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665 Posts
Discussion Starter · #7 ·
defroster

what i think ill do is drive down to opels unl one of these days and pick up the rear defroster glass and order the light that goes in the dash from opelgtparts and then just get the wire and relay from my local autozone or napa store. also what is oana never heard that abreviation befor. thanx for the help every one
 

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OANA

OANA is the Opel Association of North America, at:

http://www.opel-na.com/

Go there for all sorts of VERY required reading, such as articles on converting to rear brake disks, GM V6 conversions and such. There are also many illustrations of Opel systems, such as body panels and the GT headlight system. Go there for downloadable wiring diagrams, and ESPECIALLY the "Definitive Opel GT Guide for Year, Color and Parts Identification". JUST GO THERE!
 

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Had the car out today in the rain and noticed it would be very helpful to have a rear defroster. Are there lines or something in the rear window, original, to tell if my car already has that option?? Also one of the posts mention a little light "blue" under left vent in dash. What exactly is this?? I have a light there, not sure of color cause it doesnt come on, with one black wire hooked up to it.

Jennifer
 

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Found relay and black wire in rear with copper connector. Where does it connect to? the grid?

There is no ground wire, but something easy enough to do it I know where it connects to.

I would love to get this hooked up.

Any help is appreciated
Jennifer
 

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Yeah, black power wire to the left side of the grid, ground the right side, check to see the fuse on the relay is good, THEN hit the switch on the dash, and see if that blue light is lit. THEN hope to God that the none of those "lines" on the glass that make up the grid are scratched deep enough to break the circuit--they can be repaired, but it's a PAIN to do this with the backglass installed. Bitter experience speaking--I've had to do this before, and don't recommend it. Try to be careful when cleaning the inside of that glass (that grid is at least 30 years old, and fragile), and good luck.
 

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101st Airborne 1/327 Inf
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Rear Heated Glass Issue

I have a 73 GT without the factory GT heated window, and no Heated Glass relay behind the fuse block. I also notice that the red/gray wire from the console switch was not on the YELLOW FEMALE connector side to the fuse block. I have had a replacement window with the factory heated grid in the glass for a couple years and want to install it before Carlisle in May. I have read this post from 2003 on this subject, but still have a few question, if you folks don't mind?

1. If I use a single pole Bosch 30/40 amp relay, what
pin (30,87,85,86) would receive what COLOR wires?

2. Can I connect the light blue/white wire from the
YELLOW male side connector, right to the bosch relay?
Could not find that wire in the fuse block, or on the
D+ terminal on voltage regulator.

3. Did/do not have a indicator light for heated glass
on. Would I need that function to get this issue
resolved?

******I have attached a color 1973 GT wiring diagram to assist.*****
 

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Super Moderator
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I have a 73 GT without the factory GT heated window, and no Heated Glass relay behind the fuse block. I also notice that the red/gray wire from the console switch was not on the YELLOW FEMALE connector side to the fuse block. I have had a replacement window with the factory heated grid in the glass for a couple years and want to install it before Carlisle in May. I have read this post from 2003 on this subject, but still have a few question, if you folks don't mind?

1. If I use a single pole Bosch 30/40 amp relay, what
pin (30,87,85,86) would receive what COLOR wires?

2. Can I connect the light blue/white wire from the
YELLOW male side connector, right to the bosch relay?
Could not find that wire in the fuse block, or on the
D+ terminal on voltage regulator.

3. Did/do not have a indicator light for heated glass
on. Would I need that function to get this issue
resolved?

******I have attached a color 1973 GT wiring diagram to assist.*****
Thomas;
I don't know about the relay issues, but, the GT, when it came equipped, had a red led just under the driver's side vent on the dash. Now, just going by what I have seen over the years, and this is not just with Opels, but, every car that I have had or seen with a heated back window, ALWAYS had a indicator light, and it was either on a timed relay (meaning it would cut itself off after a set time) or if the ignition was turned off, it (heated back glass) would turn off, BUT, would not start up when the key was turned on, you had to press the switch again
 

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101st Airborne 1/327 Inf
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1,322 Posts
Thanks for the quick response Gene, but when I got this car in 2003 I noticed no indicator light for the heated window switch. My first GT had the heated glass and light by the left air vent next to the steering wheel. Would those GT's without the heated window not be fitted with completed wiring, relay, and indicator light?
 

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The original relay and wiring are not all that rare, and the short fusebox accessory wiring harness can be found used in many places. A little work at the rear of the car can connect the harness to the glass.

But even when power is supplied over 90% of the time the original glass won't defrost, because the thin internal 40-year-old elements have been corroded by the combination of sun exposure and moisture.

A new defroster glass from Europe will work, but the result of having a rear window which clears up in 10-15 minutes time doesn't really justify the hundreds of dollars in part and shipping costs it takes to make it all work. The aftermarket units can be made to work, but in my opinion they look really unattractive.
 

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101st Airborne 1/327 Inf
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1,322 Posts
This is where I am as far as wiring.... from the heated window grid to where I will mount the relay, its there and ready to connect, from the console switch to the relay mount the wire is ready, from the fuse block to the relay, the wire is ready. My six million dollar question(s) are the light blue/white, and the little indicator light with ground. Do I need that indicator light/ground? What about a possible timer that turns off the circuit after a set time??? I have read the diagram a bunch of times and saw no timer. I just want another way to create this function with the bosch relay. I HAVE A GT REAR GLASS WITH THE GRID IN IT..... Do not want to stick a aftermarket defogger on it.:yup:
 

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Just Some Dude in Jersey
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15,702 Posts
De-fog but no de-ice

My old yellow GT didn't come with the heated rear glass, so I installed two 12V computer muffin fans from Radio Shack in the back deck. When the back window would fog up on a long rainy drive or make out sessions with a babe, I would turn them on. They were pretty silent and the moving air over the glass would stop moisture from condensing on and fogging the glass. No help with de-icing, though.
 

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1000 Post Club
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4,118 Posts
Here is the experience I have with the rear defog. My '72 came with it.

The small indicator is a regular clear light bulb, not LED. It is located under the left hand vent. It will only activate when the engine is running. Even with the ignition in the "on" position, but the engine isn't running, it won't activate. When activated, it the indicator stays on all the time. It doesn't have a timer like the newer cars.

I don't know how effective the grids are because where the electrical tabs are "soldered" onto the rear window, mine have come off. I haven't really looked into how to reattach them as I don't normally drive it in the salt season, so I really don't need it. If there is an electrically conductive glue out there, I may try to reattach the tabs.

Thomas, I can look at the extra fuse boxes and extensively cracked dashes I have. If the parts are there, I'll send you a PM or reply on this thread.

Jeff.
 

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101st Airborne 1/327 Inf
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1,322 Posts
Thanks Jeff,
I really don't want to drop my fuse block to search for the light blue/white wire that runs and connects through the yellow connector. If you run into the heated glass relay send my a shout out. Hey Jeff, what started all this was the flog light switch you gave me in Carlisle. And yes, it has been installed with the fog lights and working nicely.:yup::yup::yup:

G-man,
Nice thought about fans in the rear window, but..........no.
:haha:
 
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