I've not successfully joined any! I will try as suggested by Chaz88 and yourself. I've been trying how I would normally solder 'new' wires, tin each each wire to be joined and then fuse together with heat.

For my injector loom I used new wires and plugs however, I couldn't find the main plug which connects back to the loom so here I need to connect all my new wires to the existing wires coming from my plug...Good luck me!