I just went thru this. I'd recommend finding a very large soldering iron (not a gun) or a small butane torch. The trick for me was to solder with NO wind and clean & tin the tip requently & use small clip on heat sinks that look sorta like nail clippers on either side to keep the heat from traveling & melting the insulation and getting the joint hot as quick as you hold it secure/TIGHT/steady & working with clean wiring strands all to avoid burning the wire dark which hinders heat transfer. EDIT missed the gauge you are working with yes you need a butane mini torch