85' Carrera Rear defroster not working.... where to start?

[rxtrom]

Hello all.

Nothing worse than having a frosted rear window in the morning.. I purchased this 85' Euro Carrera in August and the rear defroster probably never worked. Is there something common that goes bad in these cars to check or a good place to start?

I have never attempted to troubleshoot any electrical issues in any car before. I have a cheap radio shack multimeter but do not know how to use it.

Thanks in advance.

[86 911 Targa]

Originally Posted by rxtrom

Hello all.

Nothing worse than having a frosted rear window in the morning.. I purchased this 85' Euro Carrera in August and the rear defroster probably never worked. Is there something common that goes bad in these cars to check or a good place to start?

I have never attempted to troubleshoot any electrical issues in any car before. I have a cheap radio shack multimeter but do not know how to use it.

Thanks in advance.

pm sent.

[brianlay]

With all due respect, one of the main purposes of this forum is sharing information.
Many folks here could use some instruction on proper troubleshooting techniques.

[rxtrom]

Originally Posted by brianlay

With all due respect, one of the main purposes of this forum is sharing information.
Many folks here could use some instruction on proper troubleshooting techniques.

I sent my number to Gerry through PM. Maybe its easier for him to explain over the phone. I will reply back with my findings once I get to the root cause.

Thanks.

[porschenut]

Originally Posted by rxtrom

I have never attempted to troubleshoot any electrical issues in any car before. I have a cheap radio shack multimeter but do not know how to use it.

Then the first place to start is to learn how to use a multimeter and how to troubleshoot electrical issues. Sorry for the flip response, but a little tough love is needed here.

But I'll throw you a bone. Always, always, ALWAYS start by checking the fuse for the circuit. It's so quick and easy it's surprising so many people don't bother to start with the obvious thing. Then, check the relay. Don't know how? Learn how. There are excellent books out there on automotive electrical systems and troubleshooting. I have several.

You also need to get the electrical wiring diagrams for your car. You can't do any serious troubleshooting without them. You MUST know all the elements in a circuit in order to diagnose an issue.

Your problem could be anywhere from the dash switch to the defroster elements in the window. If your rear window has ever been out of the car, there's a good chance the defroster wiring was never hooked back up to the window connections because it's a PITA to do so.

BTW, I can think of a lot more things worse than an inop defroster. I'll bet 75% of aircooled 911s don't have operating defrosters.

[hastighet]

I am not an expert by any means, but I have recently replaced the rear window seal. The harness is in the engine bay and it's easy to forget to connect that after struggling with the install. Also check the relay back there.

Have you tried both settings? You should be able to rotate the knob. That would be where I would start.

[RSBob]

Check for breaks in the heating element lines which occur in 30+ yo cars. My 82 has 3 intact lines which is probably about normal unless your car lived a pampered life. Repairing the broken lines takes mad skills unless someone here can share their technique.

[rxtrom]

Thanks for the responses. I realize I need to delve into automotive circuitry at some point so here I am and will deftly learn how to use a multimeter in this process if it is required.

I will start with the fuse and getting my year's wiring diagram.

Hastighet,
With regards to "both settings" The defrost knob pulls in and out, I did not think it rotates. Why the multiple settings if it does?

Thanks

[hastighet]

I don't have access to my car right now, but I seem to remember there was a push/pull state and a rotate state. Maybe the rotate is the mirrors? I always thought this was a two stage system, maybe I am mistaken. I think I've only used it once.

[GH85Carrera]

The rotate is for the rear view mirrors.

Just pull out the knob to make the window defogger come on. Rotate to turn on the outside rear view mirrors. After 21 years of driving my 911 the first time I have ever used the outside mirror defogger was this summer up in Vermont. I am happy to report they work!