Electrical Question: How do I connect, do I split cables correctly?

Hi, may sound stupid but: How do I connect, split, etc I actually connect OE cables correctly? Because so current thieves (cable terminal connectors) are a very modest method – https://www.pollin.de/p/cable terminal connectors-1-5mm2-10-stueck-450294 If I want to open a completely new circuit, I can make one from fuse by current brancher. – https://www.pollin.de/p/…cherungs-stromvers-ato-standard-851422 But, how do I deal directly with cables for relay switchingun Is it possible to switch my control signals and/or my loads on them? Breaking out and crimping again with several cables often does not work with OE plugs and cables. By soldering iron you get very bad to the thin cables which are placed in the thick cable strands at unattainable places also not without melting everything else. Suggestions?