Chris
is that the screw on the back with the head or the thread on the right with the nut on it?
Matthew
Matthew, the earth is quite obvious, it has the folded brass connecter. As per your description the one with the exposed thread - it is actually a double ended bolt with the lower thread going through into the clock frame mechanism. Removing it, and cleaning the contact surfaces might be all that's needed. I've found that if you use a female connecter it fits snuggly onto the exposed thread for a good earth contact.
I had another success getting a second clock going using the same technique, but alas it appears to have a stripped cog on the pendulum drive
Cheers
Chris