I also had a 1973 mk3 cortina, the doors could be opened by just about any key so to try to prevent it being stolen I used to remove the centre lead from the distributor so it wouldn't start, lost count of the amount of times I found it 100 yards down the road where car thieves had given up after trying unsuccessfully to bump start it. Once got it stuck in the sand at Weston supermare beach and had to have it towed off. One time it wouldn't start, turned out the points were fried, picked up a set and refitted but had no feeler blades to set gap, turns out the card off a cigarette packet was just the right thickness for setting the gap(wise old fella showed me that) Lots of fond memories of that old nail (most of which I can't share) but it eventually gave in to the dreaded rust and ended up in the local scrap yard.....glad I moved on from old bangers