After filling up the tank on Saturday my fuel gauge stopped working and just reads zero, tested the wires coming from the fuel sender and the gauge moves up to full works so that still works. could it be the internal mechanism inside the fuel tank?

you should be able to test that in the car but i cant recall how    -    i think to get at them you have to take the tank out -

If you've grounded the wire that goes between the gauge and the sender and it goes full scale in can only be the sender unit.. Trouble is MkII senders are not that easy to find.. :(

I did some experimenting a little while ago with rewiring the card inside the fuel sender, you'll know what I mean when you pull it out, they call it the 'card'... I purchased resistive nichrome wire from ebay, I forget which guage but I have it in the shed and I can check it. Mine is still not working correctly, I think it needs to be wound on very neat so the wires dont actually touch... I'll have another go someday when I get time, just a messy job with fuel going everywhere.

You can get the senders fixed by an instrument specialist.  Not sure where you are but in Melbourne there are a few around. Howard instruments in Heidelberg, Ringwood speedo services.
 
You dont need to remove the tank to get the sender out either. Just run it low on fuel before you do it or you will have fuel everywhere!
 
 

I just dropped off a RS2000 dash to Ringwood Speedo's to get the Tacho, Fuel & Temp Gauges sorted.  They were half the price of Howard Instruments.  The old boy there is a bit crotchety but knows his stuff.
 
Cheers,
 
Matt