Radio / wiring

[coopman]

So, whilst I was checking the power to my cigarette lighter, I stumbled upon a random coaxial cable. This was particularly interesting, because although my head unit appears to be in good working order and plays cassettes fine, there's no radio reception - I'd previously checked the aerial connections and although they were a bit messy, everything looked ok.

Anyway, I dug a bit deeper and there's loads of spare cable under the gear shifter (see pictures). It's routed into the passenger footwell and round towards the door, so I assume it eventually goes back to the aerial at the rear. There are also some additional taped-off wires (red/black and purple) hanging out of the centre console.

Before I take apart the entire car - can anyone tell me what is going on here? Is this the cause of my radio reception problems, or a red herring? I can see from the four holes next to the handbrake that this car has (probably) had a phone installed at some point in its life... no idea how that would have been wired in.

[coopman]

More pics.

[Tzantushka]

That coax looks like '90s yuppie car phone to me.
But could be a dodgy AM radio install.

If I recall correctly the stock antenna coax is light grey in colour and goes down the LH floor pan and back to the LH rear quarter.
Also IIRC, there should be a white & red wire following the coax back to the antenna - they're for the power antenna.

OH and the black PVC tape is a giveaway.
Everything factory I've seen is wrapped in the cloth tape.

[Contours]

Hard to make out the cable from the pics but if its not an aerial, there may have been a Cd changer living in the boot at some stage.

[kdevitt]

Pretty certain its a phone kit - had to take a similar set up out of my own car.

[Brianmoooore]

As above, almost certainly the left overs from a phone. I'd check out the other ends of the red and purple wires to make sure they're still not live.
Radio aerial cable should run down the left hand sill, but they were dealer fitted, and not all technicians followed BMW's instructions, so I've seen a few where the aerial and rear speaker wires both run through the centre consoles, then under the short bit of carpet across the tunnel, before going under the rear seat.

[coopman]

Thanks everyone, it's good to be able to talk things through. So, it looks like:
1. I was looking at yuppie phone leftovers
2. The radio reception issue is not directly connected.

I've been rummaging around in the boot, looking at the aerial. As per Tzantushka's post, I've found the grey coax and the white and red wires. Assuming there was once a power aerial, it's now gone (the red and white wires therefore aren't connected to anything). The grey coax is connected to a black coax, which is joined to a manual aerial... barely (see pictures). I guess that's the answer to the reception problem, so I'll fix it.

Is it worth buying a new power aerial?

[Tzantushka]

Great sleuthing!

My car was originally a Sydney car and appears to have the same manual aerial 'upgrade' as yours.
(probably from the same knuckle-dragging mouth-breathing car stereo installer)

Firstly, good to see the power antenna plug has been left unmolested.
I think the red wire is a constant 12V+ so take care.

Secondly, you'll need to fix the coax to the antenna.
Whether or not you go back to original, that can't be helping with radio reception.
If need be, trace the coax back to the head unit to ensure there are no other surprises or dodgy splices AND it's plugged into the head unit.

If you'd like to go back to the '80s - then you'll need one of these.



Hirschmann electric aerial with the BMW specific mounting bracket and quarter panel grommet & seal.
A few BMW wreckers may have them - also found on older Mercedes as well.
Try before you buy

Most likely cheap used ones will require replacing the antenna mast by now.
That's reasonably inexpensive to do if you're handy - link here

PS - just had a good look at some of your pictures of the console near the park brake.
4 self tapper holes.
Yep - that's the calling card of the yuppie car phone!

[coopman]

The car is in good shape except for anything to do with the bloody radio. What my pictures don't show is that someone has brute-force ripped out the centre consoles at some point - the underside, beneath the vinyl is all cracked and the retainer clips are fucked.

I should have mentioned that I unplugged the coax from the antenna before I took the pic! An antenna cable is plugged into the back of the head unit. However, I haven't tracked the cable right through the car as I don't particularly want to lift the carpet and rear seats if I can avoid it.

P.S. Does anyone know if the center conductor cable in the coax is actually that tiny little strand in my picture above?? Hopefully if I strip the casing back a little I'll find something more robust!

[coopman]

Turns out that tiny little wire which is the diameter of a baby's hair is the centre conductor wire. It was a total pain in the arse fixing up the coax connection... and the radio reception is still a disaster. Oh well, Australian radio is awful anyway.

[Brianmoooore]

The design and principals of operation of coax cable is complex, but generally, the thinner the centre conductor, the better. It should also be thought of as more of a circular waveguide, especially as frequency increases, rather than a piece of wire, with the signal passing along the space between the conductors, rather than in the conductors themselves.
For this reason, it's important that the 'coaxial' nature of the cable is maintained at any joins. Separating the inner and outer conductors and twisting them together, as you might do with a two core cable carrying 12 volts, won't work without losing a lot of signal at the join.

[coopman]

I get that thinner is better, but it makes it incredibly difficult to fix once someone has played around with the original cable - especially when leaning into the boot to do it. I've tried to maintain the 'coaxial' nature, but it needs someone more dexterous than me.

[Brianmoooore]

Have you checked along the rest of the cable for dubious joins?

[coopman]

No. I've checked the two "ends" (aerial and head unit). Will need to build up some motivation before checking the rest.

[coopman]

To follow up on this:

About a month ago I ordered a really cheap Chinese power antenna off eBay (AU $32.83) - wasn't expecting much, but at that price it was worth it for curiosity alone. Anyway, it arrived this weekend, which was good timing after my existing aerial was broken off the week before. It's actually way better than I was expecting, i.e. it isn't complete junk and it works! Worth considering if anyone is looking for a budget option.

The other thing I've realised is that since buying the Continental TR7412UB‑OR, I get good radio reception regardless of whether the antenna is connected or not.

[Brianmoooore]

Looks like it even has a water drain connection at the bottom. Don't forget to fit a tube between this and the connector to the air flap behind the side of the bumper.

[coopman]

Good spot - it does indeed have a drain.

[Blanca]

Regards the original question, you can rip all that out back to source, redundant phone kit. I have fitted dozens in the early 80's. My first one was on Hutchinson, pre Orange, in 1981

[coopman]

Regards the original question, you can rip all that out back to source, redundant phone kit. I have fitted dozens in the early 80's. My first one was on Hutchinson, pre Orange, in 1981

It's all gone now - became much clearer what was going on when I re-wired the stereo. Quite satisfying ripping it all out.