Replacing a 2 gang dimmer switch

I'm currently trying to replace a 2 gang dimmer switch. I made (i thought!) a careful note of where the wires should go (there are three red wires: one went to the c terminal of the second gang, one to the first gang L2, the final one to the second gang L2 terminal, with a further red wire linking the L2 terminals on each gang) but when I tested it one of the lights switches on and off fine, but the other stays on all the time!

I've compared it to another 2 gang switch in my house, but that one has 4 red wires, with a different red wire attached to the c terminal on each gang, so I can't wire it up in the same way. Any ideas?

Are you sure that the link wire didn't connect the two [C] terminals?

And do you have anything (e.g. meter) that will enable you to identify which is the permanent live?

Thanks Ban - connecting the two C terminals has solved it! Your help is much appreciated.
PS Excuse my ignorance, but if I'd wired up the live wire to a L2 rather than C terminal would this be a problem/ would it still work ok/be safe?