I need to install a fitting in place of the oil pressure switch but I don’t know the thread type lm thinking M14 but not sure.So please let me know if M14 is right.

Midwest Bayless lists it as 14mm X 1.5

Gauge Sending Unit:
https://www.midwest-bayless.com/Fiat-12 ... 50-oe.aspx

Warning Light Sending Unit:
https://www.midwest-bayless.com/Fiat-12 ... e-nos.aspx

Port Doubler:
https://www.midwest-bayless.com/Fiat-12 ... s-new.aspx

Thanks for clarifying that and merry Christmas