I decided to try solder seal butt connectors to tie into the factory wires, mainly because they claimed to be waterproof. But I soon found there are more reasons to use them instead of traditional ...

“First, ensure that the bits of wire you want to solder are touching. Obvious, really,” said Knott. “It’s easier to handle a small bit of solder wire, rather than the entire reel of solder ...

I now have a pre-heater and hot air, and if there are connectors on the pcb I can use low melt solder (4.50 euros for 17cm wire) or heat the pcb from the bottom, which may result in burn marks.