The switch isn't supposed to hiss. Rebuild the thing and the problems should go away, unless there is something else that is broke.
Basically there is a rubber diaphram that needs to be replaced. It is pretty simple to do but I decided to let Hervey rebuild it. I'm not sure what DMCH sells the part for but they do have detailed instructions on their support site if you choose to use their part.
Top Roman Steve aint stupid but that was the closest thing to a "what he said" smiley I could find....
eBay selling at it's best I can tell you stock Delorians and quite a bit of slugs so the Turbo is a super nice up-grade.
K-Jet: Causing electrical issues since November 5th 1955