Mk IV Nav Location Off, "Satellites 0"

[BigLion]

Hey guys - long time, but I've been replacing a bunch of parts in the cooling system in all my spare time which is fairly elementary stuff....

but I had to replace the Nav unit (Mark IV) as it suddenly stopped showing the location after 10 years of trouble-free operation; the 'new' unit was Ok in the first instance, but I gather it has a non-volatile memory which will tell the Nav it's last location, but then it drifted further and further off until the location point is now in the ocean

I opened the Service menu and under 'Sensor Check' it says
GPS Satellites: 0
GPS Status: Reception interf.
Gyro: 02511

I don't remember there being an antenna cable being connected to the previous Mk IV unit when it was removed; do the red and blue connectors handle that?? I followed all the cable looms and there is no spare/ unconnected Coax/ antenna cable hanging around

What shall I try next to restore my GPS Satellite positioning???