Rear window defrost not working

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cmcgettrick
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Rear window defrost not working

Post by cmcgettrick »

Hey Guys,
While I had the HVAC panel out I figured I would do a little troubleshooting on my rear window defroster that doesnt work. The switch lights up when I urn the headlight on but does not light up when I push it in to turn it on. I have checked the fuse in location 20 and it is fine. I also checked for continuity on the switch itslef thinking it might be bad but it also works as it should. So I wanted to know if there is a relay for the rear defrost, I cant find anything that specifically says there is one. My car is a 1988 M6.
Thanks again for the help.
Chuck
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Re: Rear window defrost not working

Post by Sbeaud »

I don't think so. Here is the circuit.

Scott
1988 BMW Rear Defog Circuit.jpg
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Re: Rear window defrost not working

Post by cmcgettrick »

Thank you for posting this Scott. I have very limited experience reading wire diagrams so Im pretty sure Im not reading this right either. I see at the top of the page that there are 2 fuses in the power distribution box, fuse 8 is a 30amp and fuse 23 is a 7.5 amp. Im guessing the power distribution box is the box under the hood. So in the owners manual it states that fuse 20 is for the rear window defrost and should be a 30amp fuse. It also states that the spot for fuse 8 is not used (see pics below). Again Ive probably got this all wrong which is why I am asking.

Thanks again for the help!
Attachments
Fuse locations.jpg
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Re: Rear window defrost not working

Post by Sbeaud »

Interesting. Below is the manual I have been using. It is dated 1988. You note you have a 1988 M6. Is it an M6, or a M635?

Scott
1988 BMW Fuse Box Owners Manual.jpg
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Re: Rear window defrost not working

Post by Sbeaud »

Owner Manual
1988 BMW Fuse Box Owners Manual - 1.jpg
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1988 M6
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Re: Rear window defrost not working

Post by cmcgettrick »

Thanks guys! We might be getting closer to an answer.
Scott - your manual is definitely different. Its interesting that fuse 8 states it for the rear defroster but doesnt list what fuse should be used in that slot.
wfwright2 - based on the manual that Scott provided, slot 20 should have a 30amp fuse and it sounds like 8 should also. Yes my car is an 88 M6 (1011 7/1987)

Here is the pic of the manual that came with the car. Seem strange it would be incorrect because all of the other manuals have the original owners info in them so it would seem strage that the manual got seperated from the group.

Thanks again for the help with this.
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Chuck
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Re: Rear window defrost not working

Post by 86_6series »

So, you posted this problem on Bimmerforums July 5th @ 9:03 AM
Then you post on Big6Coupe @ 1:26 PM the same day.

It would be a great help if you mention the duplication on both sites.
So, I didn't see your posts on Big6Coupe, I did searching on your problem
duplicating assistance you received from other members.
Not nice.

I'll post this on Bimmerforums to stop any more duplicating.

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cmcgettrick
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Re: Rear window defrost not working

Post by cmcgettrick »

Not nice?! What are you talking about?? I am a longtime member of the vintage Corvette community and have always posted on two separate forums when asking for assistance from fellow members. There are plenty of people who frequent one forum over another and often times one will receive different insight from different people. I have never been told that I cant post to multiple forums before and didnt realize that there is some unwritten rule that you cant do so with BMW forums. Last I checked bigcoupe and bimmerforums are independent sites so I'm not sure what I did wrong.
If I truly did something wrong I apologize to everyone that I offended, I did not intend to do anything other than pick the brains of those that have far more experience with these cars than I do. If posting to both forums is considered unethical then I will gladly stick to one forum and considering one is a pay to play its pretty easy to decipher which forum Ill use.

To those that responded, I greatly appreciate the assistance you provided. Thank you.

Chuck
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Re: Rear window defrost not working

Post by Ralph in Socal »

FYI Chuck. There is no such rule at this forum. I feel for anyone without tthe experience to complete a task. It's great that forums as BC exist to provide a valuable source of information and assistance. Post and ask away

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Re: Rear window defrost not working

Post by 86_6series »

OK, maybe I jumped on your case. But, being a long time contributor to help solve problems- I spend about twenty minutes trying to
figure out the ETM circuit on a 1988 M6 that does not have a 20 fuse for the defroster. It's ok that you may have had the wrong info,
so alerting us that it's double posted can give us additional info on what was already discussed.

I stand corrected, I should have PM'd you. I didn't have my morning scotch so I wasn't thinking clearly.

Let's start @ where the info left off and see if we can figure out the solution.

Of course I'll mea culpa on the other site.

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Re: Rear window defrost not working

Post by cmcgettrick »

86_6series wrote: Wed Jul 06, 2022 7:45 pm OK, maybe I jumped on your case. But, being a long time contributor to help solve problems- I spend about twenty minutes trying to
figure out the ETM circuit on a 1988 M6 that does not have a 20 fuse for the defroster. It's ok that you may have had the wrong info,
so alerting us that it's double posted can give us additional info on what was already discussed.

I stand corrected, I should have PM'd you. I didn't have my morning scotch so I wasn't thinking clearly.

Let's start @ where the info left off and see if we can figure out the solution.

Of course I'll mea culpa on the other site.

Bob V
All good Bob. Going forward I will be sure to make a note alerting everyone on both forums if asking the same question. Thank you.
Chuck
1988 E24 M6
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Re: Rear window defrost not working

Post by ron »

Just making a point.

The E24 handbooks are notorious for printing false information regarding fuse positions and ratings.

A couple of times I found the best way of checking was removing the fuse to see what didn't work.
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cmcgettrick
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Re: Rear window defrost not working

Post by cmcgettrick »

Ha! Yeah Ron that is what I am thinking right now. My fuse box never had a fuse in the #8 position (at least while I have had it) so Im inclined to just install one and see if that fixes my issue. Ill test continuity of the harness this weekend but unfortunately I sent my cluster out to be restored and Im not sure I can power up the car with the airbag removed to test if the fuse solves the problem.
Chuck
1988 E24 M6
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