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biotex
Samba Member
Joined: January 22, 2014
Posts: 316
Location: Alpine, TX
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 Posted: Sat Mar 01, 2014 3:49 pm Post subject: rear window defroster relay? |
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Looking at the wiring diagram for a 71, I don't see a relay in the mix. Doesn't this mean all the amp draw goes through the switch? Seems like there should be a relay.
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kreemoweet
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Joined: March 13, 2008
Posts: 4124
Location: Seattle, WA
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| Posted: Sat Mar 01, 2014 4:02 pm Post subject: |
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So put one in if you so desire. VW didn't.
Do you actually have a functional defroster grid? That would be rare.
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biotex
Samba Member
Joined: January 22, 2014
Posts: 316
Location: Alpine, TX
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| Posted: Sat Mar 01, 2014 5:36 pm Post subject: |
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| kreemoweet wrote: |
So put one in if you so desire. VW didn't.
Do you actually have a functional defroster grid? That would be rare. |
I have not ohmed it out yet. I'll wire it up even if it doesn't work though.
Reason I ask about the relay, is I ordered a switch and relay, thinking it had one. I was surprised to see it didn't. makes it a bunch easier to wire up for sure. I guess they made the switches extra heavy duty to handle a load. Sure don't see that anymore these days.
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busdaddy
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Joined: February 12, 2004
Posts: 53108
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Sat Mar 01, 2014 6:34 pm Post subject: |
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It is a really good switch but in the interest of lightening the load on your ignition switch and wiring to the front a relay at the back powered from the battery would be a good idea, I've never had a defrost grid that worked so my switch operates the booster fan in the heat duct and the gas heater I added.
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1967250s
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Joined: May 02, 2007
Posts: 2137
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| Posted: Sat Mar 01, 2014 8:47 pm Post subject: |
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| Only 8 amp, fuse #11 on my '72, for rear defrost, might draw 4 amps, probably less, as the fuse also supplies flasher and instrument lights. Not sure, but I think the rear window heating element was painted on as it is very thin. |
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cmonSTART
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Joined: July 15, 2014
Posts: 1915
Location: NH
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| Posted: Thu Nov 27, 2014 9:13 am Post subject: |
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Sorry to dig up an old thread, but does anyone know of a replacement or substitute for the rear grid? I want to use something that's close to OEM if possible, being electric and using the stock switch.
Thanks folks! Happy Thanksgiving!
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cmonSTART
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Joined: July 15, 2014
Posts: 1915
Location: NH
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| Posted: Thu Nov 27, 2014 9:26 am Post subject: |
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Nevermind, found Frost Fighter in another thread - always find what I'm looking for right after I post a question.
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75 Westy FI noob
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Joined: November 04, 2022
Posts: 490
Location: MidWest
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| Posted: Wed Oct 22, 2025 11:50 am Post subject: |
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| busdaddy wrote: |
| It is a really good switch but in the interest of lightening the load on your ignition switch and wiring to the front a relay at the back powered from the battery would be a good idea, I've never had a defrost grid that worked so my switch operates the booster fan in the heat duct and the gas heater I added. |
Do you have a Thread showing this aux fan setup BD ? that's a great idea, although I don't have a gas heater.. an extra fan in the system would certainly help the front defroster work better.
Winter is coming ! |
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SGKent 
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Joined: October 30, 2007
Posts: 42876
Location: at the beach
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| Posted: Wed Oct 22, 2025 12:35 pm Post subject: Re: rear window defroster relay? |
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there is a paint that can restore breaks in the grid. One can use a probe to a small piece of aluminum foil to look for breaks. Sliding the foil across the window will not further damage the grid. A couple pieces of pin striping tape on either side of the break to control grid line size, and paint. Fixed. New heated rear windows are available in the UK but I don't know of anyone here who sells them. If one has the later green tinted Audi VW Duro glass that helps keep glare and heat down, I have never found one.
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busdaddy
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Joined: February 12, 2004
Posts: 53108
Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Wed Oct 22, 2025 1:39 pm Post subject: Re: rear window defroster relay? |
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Sorry, no pics that I can find, it's mid way in the pipe under the cargo floor. Mine's an all metal squirrel cage blower from a 60's Datsun so finding a duplicate might be a challenge. The bilge blower requires much less plumbing since it's axial flow, the challenge is finding one that can stand the heat.
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lil-jinx
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Joined: August 14, 2013
Posts: 1752
Location: New Brunswick,Canada
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| Posted: Wed Oct 22, 2025 5:08 pm Post subject: Re: rear window defroster relay? |
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bus daddy is the squirrel cage blowing fresh air into the duct or it it pumbed to just move the air in the duct,,and would an ambulance fan in the duct work,and could it eliminate the aux fan in the engine compartment .
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busdaddy
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Location: Surrey B.C. Canada, but thinking of Ukraine
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| Posted: Wed Oct 22, 2025 8:52 pm Post subject: Re: rear window defroster relay? |
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Moving hot air in the main duct, a plastic ambulance fan would likely melt.
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lil-jinx
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Location: New Brunswick,Canada
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75 Westy FI noob
Samba Member
Joined: November 04, 2022
Posts: 490
Location: MidWest
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| Posted: Thu Oct 23, 2025 7:49 am Post subject: Re: rear window defroster relay? |
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| busdaddy wrote: |
| Moving hot air in the main duct, a plastic ambulance fan would likely melt. |
This answers my question in another thread about whether the Accordian Tubes are necessary and what material is inside them. I guess it's a kind of .. asbestos for heat tolerance? I'm going to put the heater controllers thingys back in because.. anything beats facing the next step; rust.
Oh speaking of installing the hot air control box thingys .. Does the exhaust have to come down in order to install the two metal 'up pipes' ? ( the ones that rise up from the heat exchangers )
sidenote, my green light doesn't work in my Def Switch. I liked that green light. |
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raygreenwood
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Location: Oklahoma City
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orwell84
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Joined: May 14, 2007
Posts: 2795
Location: Plattsburgh, New York
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| Posted: Fri Oct 31, 2025 5:32 am Post subject: Re: rear window defroster relay? |
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I don’t think my rear defroster has ever worked. I tried to fix it once and traced the problem to the grid wires. I might repair it someday just to be able to say it works.
Interesting point about relays. Modern cars seem to have a relay for just about everything. VW may have deemed them unnecessary because most of the switches are so rugged.
Years ago, I bypassed the ignition switch (replaced in the early 90’s) because it stopped working. The automotive style toggle switches I have used for the coil circuit seem to become unreliable after awhile causing all kinds of sudden electrical problems in spite of good wiring. I have considered using a relay for the coil and reconnecting to the ignition switch (which actually still works). |
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