dad had a problem with his ef wagon, squealing noise and alternator light comming on. Put a reco alternator on and the voltage still fluctuates as it wants. Starts and sits round 14 then drops right under 10v then can go up or down as it wants. Took it for a drive and it cut out on me several times, when the voltage drops too low all display on the dash dies, no speedo, lights etc, till eventually the motor even dies. then takes for ever to jump start it.
Renewed the battery and still the same problem any help would be much appreciated.

sounds very sick!

Check the earth strap on the block near the alternator.
Also the alternator earths itself, so make sure its tight.
inspect fusible links in the enginebay and spray a bit of crc on the connections.

Renewed the battery or replaced with another second hand one?

By the sounds of it, somethings draining a lot of current. all I can think of is the Thermo Fans, AC Clutch + Fuel Pump, as they're some of the main highest draining factory devices

And last of all.. what was the last thing changed on the car prior to said complications!?

yea, sounds like an bad earth somewhere.

check your battery terminals for corrosion, i had sorta same problem. i would clean the terminals and jump start the car. would be sweet for a while then would happen again. so i thought it was just a drain.

put new terminals on as they were causing the corrosion. seems to be fine now.