Step 10   On the units with the spring if not already done i like to solder a wire from the top of each finger pair just incase the   
               original housing loses contact. 

Hopefully in the photo you can see the black furry coated wire should be added if not already there (Also good to test for continuity if wires are already connected just to be sure)

Look at the base of the pins and you can see the original link which used contact with the casing on the finger to conduct but 30 years plus of use this may not work as well as it used to