I am replacing heat-only 2-wire mercury thermostats with Honeywell DH1100DV Pro1000s. There are two wires, red and white. I cannot tell from the installation manual where each goes in the series of slots and how they are fastened it place. There are 8 slots. The top one and the four bottom ones are empty,and the other three just have holes where the wire presumably goes. But none of the three are marked R and W, and there are no screws. Where do the R and W wires go and how are they held in place?