Which FPSS do I need, whats the difference?

[badass88gt]

For a carb'd car, I understand I use the lower pressure switch. Which one do I use though, I see a couple of them? Do I need Normally Open or Normally closed, and what's the difference?

http://holley.com/15660NOS.asp

http://holley.com/15670NOS.asp

http://holley.com/15750NOS.asp

[Evil Greg]

The N/C or N/O just depends on how you plan to wire the system. Normally closed switch completes a circuit unless the switch activates, and normally open completes a circuit upon activation. So if you use a NC switch, your system will arm whenever activated, unless the switch senses the low pressure and opens up.

[badass88gt]

Thanks.