Misfiring and electrical problems

[Flying Toaster]

So I start my car this morning (Peugeot 106 1.1 MPI) and drive off, only for it to start misfiring and engine light came on. Decided to go home and leave it there for the day and sort it out later. It's a problem I've had before when it's been cold and particularly damp but thought a new battery fixed it. I've checked it with a multimeter and the alternator was making 14 volts, although strangely I tried it again just after starting it and it was only showing 12 volts. Then the engine laboured a bit and it was then showing 14 again. Is that normal?

I Plugged in the OBD scanner and got P0300 multiple cylinder misfire which didn't tell me anything i didn't know.
Also when I've had these problems before the instruments froze in place and the lights went off, the wipers go slow and occasionally get a flickering battery light. Oh, also when I put the key into the first position to put the radio on sometimes the battery light shows, sometimes it doesn't.

Also not sure about the coil pack. Sometimes stutters when cold.

So, I'm thinking there's a bad earth somewhere or maybe the alternator's weak. Anyone have any ideas?

[S0 What]

Check/clean the earth points, had this a fair bit with french cars, mainly pugs where the earth snaps on the gearbox terminal.

[Flying Toaster]

Had a look and the one on the gearbox looks ok, the one from the body has some slight rust though. Not so sure if it is the problem but I'll look further anyway when i get the chance.