I got fed up with changing mine they don't last 5 minutes and like Newboy says you have to disconnect everything that passes through them.
So I came up with this simple solution.
Interesting info if you've 1/2 hour to spare!!
http://www.nexusmagazine.com/articles/ulp1.html
http://www.amsoil.com/articlespr/article_2...ard_motors.aspx