If you have a Cherokee with the panel mounted compass at the far left of the panel
(Flite Liner, possibly others), you may need this and just not know it. The influence of the alternator output cable on that location is rather surprising. Check the difference in compass indication between full alternator load and no load. Your compass may be fine but the windshield mounting hardware alone to get your compass out of that location is worth the $40. An alternator failure on a cross country would cause a significant error in what is normally the most reliable instrument available.