ford transit van 1997 radio

[peter354]

 

hi  am posting here as there doesn't seem to be a section for transit vans  ,but hopefully someone might be able to 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 photo included is of the ribbon cable plug

any ideas