I am about to fit capri clocks to my car but on wireing its got 2 wires that say common feed.what does that mean?
are they both earths?or are the both live feeds????

Well, I don't know anything about the wiring on Capri clocks in particular, but in electrical terms a 'FEED' is a supply, i.e +v.

Some (very) old cars were postive chassis, but I doubt a Capri would be. But it could well be that the associated switches etc were switched positive, where as later Fords were switched negative. Either way might be best to buy or try and download the wiring diagrams for the capri.

Older fords were positive earth so there is a small chance it wants to see a neg. I doubt it though and its probably a positive feed that it requires. Can you not work it out by looking at the wires and circuits?