2005 Nuevo Radio Wiring

I'm loath to start yet another radio thread but I can't seem to find an answer to this one anywhere.  After the first long-distance trip in our newly-acquired 2005 Nuevo nearly drove me to distraction (literally!) I've decided that the OEM radio has to go.  I overcame the infuriating 20-minute cut-off by keeping the radio isolation switch on for the return journey but the reception was intermittent, volume variable and fiddly to adjust, and the sound clearly not making the most of the new door speakers which I had already replaced as the original ones had perished. 

My question is this: I have shortlisted a few potential replacement head units with DAB and Bluetooth, all of which have the standard double ISO 8-pin connector block - one for the speakers and one for the various in/out power leads.   However, in addition to these, the OEM unit in our Boxer-based chassis has an additional multi-colour connector block containing just 3 leads.  I can't find any diagram or description of what these are for and whether they need to be re-connected somewhere. The drawings on the label on the old head unit identify them as: RC-A, RC-B and Earth and the wires are coloured green, green and pink, and black respectively. Can anyone throw any light on what they are for?

As far as I know the wiring on our van is original apart from a red isolation key for the hab battery fitted behind the drivers seat, with a voltage readout on the side. I have found that unless this battery is isolated the hab battery drains in a few days, even with everything else including the panel master switched off.  With the radio isolator above the fridge set to 'on' the radio power light illuminates as expected but with the hab battery isolated the radio only works with the engine running (also as expected). 

Any advice before I bite the bullet and order the new radio (probably a Blaupunkt to keep the 'retro' look) would be much appreciated. 

Many thanks
Ian Pallister

There should be an ISO connector/adapter available to connect a new head unit into existing plug/sockets. If I remember correctly, then the RC-A and RC-B wiring is something to do with breaking the connection by way of a "mute" type function when the telephone connection is activated. So you are "listening" to the telephone, rather than the head unit signal, so you hear the phone over the speakers and not the stereo.

Even when you switch off the isolation switch in the rear which allows the radio to remain on, you still must switch the radio off as normal otherwise it will still take power and drain your battery. If you wait until dark you will see the radio knobs still illuminated if you don't do this.

It's a while since I last read anything about the 20 minute timeout in the radio for Boxers of that age. Is this really how it's meant to work? I thought the problem was that the radio would time out after 20 minutes if you manually switched it on with the ignition off - is it really also meant to work that way when the engine is running?

Roopert wrote:It's a while since I last read anything about the 20 minute timeout in the radio for Boxers of that age. Is this really how it's meant to work? I thought the problem was that the radio would time out after 20 minutes if you manually switched it on with the ignition off - is it really also meant to work that way when the engine is running?

My understanding, and how my 2004 Ravenna works is this: 

Engine off, manually turning my radio on means it stays on constantly. Putting the radio cut off switch to the on position, it cuts off after 20 odd mins 

Yes, that's exactly how I remember it being described, but the OP wrote this:

"I overcame the infuriating 20-minute cut-off by keeping the radio isolation switch on for the return journey"

which suggests that they have a different problem.

Thanks all for the comments. MalMonty's suggestion that the extra socket is for a wired telephone probably rings true(!) as I've taken the plug out and it has made no difference to any of the useful radio or CD functionality.   Delving deeper into the head unit Menu also revealed a Telephone volume option which, along with three of the unused pins being marked 'TEL', would seem to back this up. I presume that a head unit with a Bluetooth telephone connection shouldn't need it so I can leave it disconnected.
 
Interestingly the Menu also has an 'Ign Time' option that is not mentioned in the Boxer manual, with a choice of 20 minutes or zero.  I've re-set it to zero so the radio turns off with the ignition but not yet had the chance to see what impact, if any, this has to the unwanted shut down on the road if the hab battery is isolated.  If I isolate the Hab I also have to input the radio code every time at turn on but at least it's not then draining the battery!