DON'T DO IT! These archaic mechanical devices are extremely shock sensitive. It is a wonder they survive even with the spring. If you take apart a dead one you'll see what I mean. The INOA Tech Digest has a schematic for making a solid state version, but I could never get mine to work (I'm obviously not an electronics tech!). I bought a unit from RGM which is solid state, but is wired differently. Seems to last much longer (3 years now).
Ron L