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Wiring for rear window defroster
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Newbie69
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PostPosted: Thu Dec 08, 2022 1:33 pm    Post subject: Wiring for rear window defroster Reply with quote

I have a 08/69 beetle sedan. I'm trying to connect electrical wiring for thr rear window defroster , I can not locate the regulater? The previous owner may not have reinstalled it during their complete rewire. Hoping for help where the regulater should have been placed?
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Cusser
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PostPosted: Thu Dec 08, 2022 1:41 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

The switch for the defogger was under the dash near the driver. The relay was under the rear seat, driver side. For USA VWs with driver on the left....
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PostPosted: Thu Dec 08, 2022 2:24 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

You need a 30A general purpose relay; it gets its power from fuse #10,at least on a '73 Super. Check the Samba technical section for the wiring diagram for your year.

Come to think of it...did '69 even have a defroster?? Think
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Cusser
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PostPosted: Thu Dec 08, 2022 3:14 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

I think 1969 was first year of rear window defroster.

I got my 1970 sedan in 1972, and I must say that this didn't seem to work very well on mine, maybe because most trips in winter were under 30 minutes.
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Newbie69
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PostPosted: Thu Dec 08, 2022 5:05 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

From the wiring diagram which I viewed for 08/69 .there is a regulater C1 that appears to be between the generator and (relay that is under back seat). Most likely not the right way, wondering if I could just run a hot straight from the B+ generator to the relay with an inline fuse? Or tap into the starter wire that is next to the relay.
Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.


All other wires that are needed for relay and defroster switch are there.
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PostPosted: Fri Dec 09, 2022 5:41 am    Post subject: Re: Wiring for rear window defroster Reply with quote

I would tap into the starter wire with #10 AWG and a 30 amp inline fuse. I never connect anything direct to the gen/alt.
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PostPosted: Fri Dec 09, 2022 7:22 am    Post subject: Re: Wiring for rear window defroster Reply with quote

Newbie69 wrote:
From the wiring diagram which I viewed for 08/69 .there is a regulater C1 that appears to be between the generator and (relay that is under back seat).


The voltage regulator under the rear seat has nothing to do with the rear defrost system. VW just used the B+ terminal on it as a convenient location to branch off the hot lead from the battery over to the rear defrost relay, since they are both under the back seat.
Since you have switched to an internally regulated alternator and are now missing that voltage regulator, I would just simply run a wire with an inline fuse directly from the battery + terminal over to terminal 30 on the rear defrost relay.
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PostPosted: Fri Dec 09, 2022 7:35 am    Post subject: Re: Wiring for rear window defroster Reply with quote

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Actually you should just be able to splice in to this wire since it comes over from the battery, and run a FUSED lead over to terminal 30 on the rear defrost relay. This would basically be the same thing VW did.
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PostPosted: Sat Dec 10, 2022 7:14 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

Read this before getting too far into it, your grid is most likely long dead.

http://www.vw-resource.com/defogger.html
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PostPosted: Sat Dec 10, 2022 7:21 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

Show of hands.

Lets see how many people have a working rear window defroster.


I have never talked to anybody that does.
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PostPosted: Sat Dec 10, 2022 8:06 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

vwracerdave wrote:
Show of hands.

Lets see how many people have a working rear window defroster.


I have never talked to anybody that does.


My '73 Super has a working rear defrost....an aftermarket window. I have an original rear window from a '71 that has good continuity across all the lines. Never had a car for it though, bought it before I learned '72 rear windows were slightly bigger.
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PostPosted: Sun Dec 11, 2022 8:32 am    Post subject: Re: Wiring for rear window defroster Reply with quote

vwracerdave wrote:
Show of hands. Lets see how many people have a working rear window defroster. I have never talked to anybody that does.


Mine worked on my 1970, purchased in 1972. At least it did work somewhat, and that was in the 1970s. I'm in Arizona desert, so there really wasn't much reason to even try to use it.

When I resurrected that VW in 2016-2017 after its retirement in 1993 I did check for continuity on its rear window grid when I had the rear window out to replace the rubber seal, and I had no continuity by then. So I just ignored that, and re-installed it with the new seal.

I wonder if there are small-enough stick-on rear window defroster grids available......they exist for larger windows....
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PostPosted: Mon Dec 12, 2022 5:25 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

vwracerdave wrote:
Show of hands.

Lets see how many people have a working rear window defroster.


I have never talked to anybody that does.



I've had 7 different VWs, and none of the rear defrosters worked.
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PostPosted: Mon Dec 12, 2022 5:33 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

Mine worked when new (1971), but not well since about the late 1980s.

What you see are the primer paint lines, not the actual conductive/resistive material, which likely has long since evaporated.

They were always treated gently, it was just a poor electrical/mechanical design that can't last. You'd be far better off with a small forced air heater aimed for best effect, using the same wiring and relay.
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PostPosted: Mon Dec 12, 2022 6:37 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

KTPhil wrote:
You'd be far better off with a small forced air heater aimed for best effect, using the same wiring and relay.


That sounds like a really good idea...any particular heater/fan in mind?
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'75 Super Le Grande...waiting it's turn in line behind '74.
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PostPosted: Mon Dec 12, 2022 7:23 pm    Post subject: Re: Wiring for rear window defroster Reply with quote

Good luck with that,Most all of them suck up to many Amps Crying or Very sad
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PostPosted: Tue Dec 13, 2022 11:22 am    Post subject: Re: Wiring for rear window defroster Reply with quote

I don't have a particular suggestion, and they are not super hot/super flow, or they take too much current. But a well-aimed air pusher, plus a little heat, might go a long way.

Maybe check the Bus forums for heater/blower suggestions, since they have well-known heater issues!
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PostPosted: Tue Dec 13, 2022 11:33 am    Post subject: Re: Wiring for rear window defroster Reply with quote

KTPhil wrote:

They were always treated gently, it was just a poor electrical/mechanical design that can't last. .


What part about the original system was the main design flaw- did the system send too much current through it, did they use bad adhesive to stick the grid to the window, etc? I've always wondered if buying one of the new windows with a new defrost grid would yield better, same, or worse results

https://www2.cip1.com/vwc-111-845-501-k/
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PostPosted: Tue Dec 13, 2022 11:37 am    Post subject: Re: Wiring for rear window defroster Reply with quote

The resistive material degraded over time, even if on the shelf, I have read.

In aerospace, we do "high temperature accelerated aging tests" to predict life expectancy. Maybe VW (or their suppliers, Sekurit, Siglia?) didn't do this back then?
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