Radio/Aerial Query

[Steve Medlock]

I'm putting the car back together rather hurriedly for next weekend and refitted the rear wings on Thursday. When I went to replace the serial base, I noticed a spark when the bracket touched the mounting stud on the inside of the boot. Investigating today, there is 10v odd at the outer sheathing of the aerial cable! At the other end, the radio is dead which I assume is a fuse blown.

But why have I got live voltage in the aerial cable with everything switched off? Is there a straightforward answer to this please or do I have a short somewhere?

Steve.

 

[colb]

There is a live connection inside the boot to the aerial unit, not sure you should be seeing voltage on the outer sheathing of the aerial co-ax cable must be a short in the unit. On mine that live connection inside the boot remains live when the ignition is off, found that out when I took mine out to repair the top where the mast screws in. The small wire inside the top had broken requiring a new wire to be soldered in.
http://www.realoem.com/bmw/enUS/showparts?id=CM12-EUR-12-1999-Z3-BMW-Z3_19&diagId=65_0284

 

[Steve Medlock]

There is a live connection inside the boot to the aerial unit, not sure you should be seeing voltage on the outer sheathing of the aerial co-ax cable must be a short in the unit. On mine that live connection inside the boot remains live when the ignition is off, found that out when I took mine out to repair the top where the mast screws in. The small wire inside the top had broken requiring a new wire to be soldered in.
http://www.realoem.com/bmw/enUS/showparts?id=CM12-EUR-12-1999-Z3-BMW-Z3_19&diagId=65_0284

Presumably that's the white wire with a plug? I unplugged that one and then unscrewed the coax and still had voltage on the coax.

 

[colb]

Something amiss at the radio end of the co-ax by the sound of it, test it at the radio end and check the radio chassis whilst your in there maybe when pushed into the dash its chaffed a live wire and the voltage is travelling down the co-ax as it would be connected to the radio chassis when inserted into the aerial socket. Surprised if the fuse has not blown.

 

[smiffy]

this all part of the numerous flat battery reports you see from people that don't drive their cars on a daily basis.

I tried to cure it in Tracey Dee's last year and had to do a bit of a fudge. I've got the same issue with mine and to date have only established that it is something to do with the negative side. As a short term fix I've ended up with a switch in the boot to isolate it.

Measured with a current meter, the drain is 0.15A (150mA) which may not sound much but is enough to prevent starting if left for a fortnight, and potentially a trashed battery. Normal drain should be around 0.03A (30mA).

In Traceys we had the stereo out and that didn't stop the drain. Looking at mine since I've come to the conclusion it is an issue in the loom but I've stopped short at cchasing through the whole loom. No the wiring drawings don't help!

 

[Steve Medlock]

OK many thanks. There's obviously not a quick fix to this so I'll try to come up with a work-around for now and investigate at a later date.

Steve.

 

[smiffy]

my temporary fix is a switch in the Brown Earth wire that is secured under one of the aerial mounting bolts in the boot.

Switch off when you park up for anything more than overnight, and just remember to switch on before you get in to drive or no music!

I will find the cause one day!

 

[buze]

I don't know if you have access to the 'contact' 12V around there, but you could add a relay that contacts only when the power is on...

 

[Steve Medlock]

This was a strange one. I finished putting the car back together yesterday and after I'd reinstalled the hood unit, i checked the coax again and no voltage showing so I reconnected it to the aerial base. Can only assume an intermittent wiring fault somewhere.

 

[mrscalex]

Be very, very careful with electrical issues. Especially in the boot.

One of my project cars is a gorgeous 2.2 Sport but with a partially melted loom. It started with a small issue with the boot light. Probably just a nicked cable touching something it shouldn't and making it live. And it nearly ended up in a fire.

It's not a scare story. There is at least one other person on this forum who has had the identical issue.

The cabling in the boot is particularly susceptible to damage. I would want to know what was causing that problem.

And yes, for all I know only a 5% risk but is it worth taking?

 

[Steve Medlock]

Sure enough but as others have indicated, Its not an easy problem to solve. For my own part, I'm now looking at a problem with no symptoms.

 

[Tracy Dee]

Probably not the same but Smiffy found fuse 9 was the cause of my horrendous drain wrecking 3 battery's in the process.
Fuse 9 supplies cd exchange which I don't have amplifier which I don't have and the radio memory which was connected to my cigar lighter so fuse 9 could be extracted.
Hey presto no more huge drain been good as gold ever since can leave it 10 days now without drain not that it's been left that long it's been used a fair bit recently but on average used twice a week without any battery issues.
Hope you get yours fixed good luck.