replacing radio in ford transit

Hi dont know if any body out there can help .have a 1997 transit van UK converted to motor caravan FORD TRANSIT AUTOMATIC 4 BERTH DUETTO AUTO-SLEEPER and am trying to fit a replacement cd radio, the original was a cassette

Have sorted out the main12v wiring , but the speakers are a mess.it uses a ribbon cable and flat ribbon cable plug which has between speakers coloured, and possibly pink of 85 ohms (bit weird )and at the wall mounted speakers 127 ohm(even weirder) so make me think i have a preamp or amp installed somewhere but dont know of one
the cable no is enclosed as jpg ( unable to include loom no )

any ideas
peter

hi thanks
as you might have expected have sent emails to many different people and hopefully will get some idea what going on  I know round about that time some company's were experimental with fibre optics ,but i think this would be too far a change for Ford at that time
peter
will keep you up to date
peter

My Duetto (1996) has a pre-amp under the dashboard, passenger side. You can simply lift the tray out of the cubby hole in front of the passenger, and there it is. We had the radio replaced by a car radio specialist, I'm not sure if he removed the pre-amp or not.

I replaced both radio and speakers in the Duetto I owned. The Ford speakers are absolute rubbish and I replaced with a pair of Alpine speakers I bought off Amazon priced around £25 so not madly expensive and the difference they made was instantly noticeable.

A word of warning. Though the speakers are elliptical the mounts are not! Ford did a very crafty dirty trick imo as the Ford speakers are moulded into a case and it's only when you remove it, you realise your new elliptical speakers are not going to fit without some considerable fettling. The only reason Ford did this was to discourage fitting after market accessories but it's extremely petty imo.

I got round it by using the moulded case to fashion a plinth from fibreboard then screwed the speakers to that. I posted a thread detailing it on here but cannot find it.