Troubleshoot this!

[NielsGalan]

The heater (demister) for my rear window quit working some time ago.

When I activate it nothing happens. The light comes on for a few minutes as usual, but no heat to the window.

Radio reception is worse now. Windshield wiper/washer interferes with radio signal now. Also, sometimes braking makes the the radio crackle for a second.

What am I looking at here? Relay under the rear seat, or are the wires back there the culprits? Any clues?

Thanks in advance.

Niels.

[Jay 535i]

Could the wires in the back have been damaged somehow? Botched tint job, maybe? It sounds like they're all broken, giving you zero demisting and zero radio reception.

[NielsGalan]

Botched tint job,
What do you mean by this?


Anyway, I don't see why the cables suddenly would become damaged.

Wouldn't "zero radio reception" mean zero sound? I hear the radio fine, but now the quality is a bit poorer and wiper/brakes etc. interfere with the signal.

[Jay 535i]

What do you mean by this?


Anyway, I don't see why the cables suddenly would become damaged.

Wouldn't "zero radio reception" mean zero sound? I hear the radio fine, but now the quality is a bit poorer and wiper/brakes etc. interfere with the signal.

If the windows were tinted and somebody got careless with a utility knife during installation, that could cause the problem. Alternatively, if tinting was removed without care, those lines could have been broken.

Actually, even if the lines are broken, you would get some radio reception, but it would be poorer. Exactly as you describe.

As for the wiper/brakes, my guess is that having those things activated is creating electrical noise which is interfering with the radio. The interference is there always, but usually the antenna is so good that the noise is easily filtered. If your radio antenna (i.e. the top few lines on the rear window )is broken then it would be more vulnerable to that kind of interference.

So I still think all your symptoms point to broken lines on the rear window. If the windows were tinted by an amateur, I can easily see how one swipe of a utility knife could cut them all.

Keep in mind I'm not an expert. There are others here that know a lot more than me. But I've given you my best guess.

[Dan in NZ]

I would suspect the antenna booster box thing that the demister goes through... In the rear pillar, I forget which side. Could have lost it's ground or something.

[Jr ///M5]

Under the rear seat driver side, is a relay/fuse block. I found a bad (melted) fuse that controlled the rear window defogger for my '89 535. Replaced the fuse and it worked fine. You might want to check under your rear seat by pulling straight up where you would normally sit between your knees. It takes a little effort, there are two catches, one on both sides.

[NielsGalan]

Yes I did check the fuses. I will have a look at them again and the relays as well before I start tearing the back of the car apart.

Thanks for your info.

[skr]

the booster box is in the right rear panel. check the conections there

[zuzuk212]

Also, sometimes braking makes the the radio crackle for a second.

Check the wires in the trunk which are on the lid support and go to the tail lights. These break and unpredictable things can happen when they start shorting to ground or each other. It may not be it, but it is an easy check.

Ken

[NielsGalan]

Hmmm. Just to close this thread (for future reference) ... I found the problem with the Heated Rear Window.

I was the fuse under the back seat under the black cover. I inspected it visually (looked ok) initially, but when measured it was burned. This excact fuse was mentioned to me in another thread (I've had this problem for a while), but I chose to rely on my eyes. So now the fuse is ok and so is the heated window (defogger).


The radio, though, still crackles when I touch the brakes ... Innaresting ...

[Jay 535i]

Glad you got it sorted!