The 20 way Molex Plugs use connections which are usually crimped, the main reason is wicking where if you labour to long with the iron the solder back tracks up the wire and can make the wire snap at the end of the solder. But saying that I have soldered various types over the years without failure and very careful use of a needle point iron. The terminals with the plastic covers I have found to be weak or weaker if the covers stripped off, there primary use is crimp, just buy ones designed without the covers which are constructed for that application. On standard 6.3mm Lucar connectors I always use the ones with the clear rubber boots which were O.E back in the day.
If you do crimp then please don't use those cheap crimp pliers off ebay, all they do is put 2 flats on the terminal and is the single most failure I see on DIY wiring, get the ratchet type/
Edited by KernowCooper, 19 April 2017 - 07:16 PM.