The way I solder heavy gauge wire and terminal lugs is as follows:
I use a MAPP gas torch, you want plenty of heat so you can do it quickly before everything gets heat soaked (especially the cable)
Have a plastic spray bottle close by, full of water and set to produce a spray that is almost a solid stream (so you can control what you squirt the water on with a bit of precision)
A junk cotton rag soaked with water is also handy to have close by.
Clean both the cable end and the inside of the terminal so they are bright.
Slide a length of heat shrink tubing over the cable end and slide it back a couple feet so it won't get too hot while soldering.
Paint the cable end and the terminal lug with some zinc chloride soldering flux.
Heat and tin the cable end -- you don't want to over heat it and melt back the insulation too much, just get a thin coating of solder on the outer surface of the cable end.
Pull the heat away immediately when you get a bright coating of solder on the cable end.
(a quick wipe with the wet rag down the insulation of the cable moving toward the cable end helps to avoid the insulation curling back and pulling away from the hot end of the cable)
After it has cooled enough to handle, dress the end of the tinned cable so it has no rough spots and is a snug but sliding fit in the cold terminal, put a bit more soldering flux on it and set it near the vice.
Put the terminal in a vice with two pieces of wood or masonite clamping the lug end so the vice does not suck all the heat out of the terminal.
Heat and tin the terminal. A bit of aluminum foil with a slit in it slid over the terminal and vice jaws will cut down heating of the vice and smoking of the wood pads)
As soon as it is hot enough for the solder to flow, stuff the cable end in the terminal and start feeding solder to the upper end of the terminal (cable end) as you apply the hottest part of the torch flame to the lower end of the terminal and end of the cable. (this takes 3-4 hands so recruit a helper if you can to handle the cable while you handle the solder and heat.)
This causes the solder to wick down toward the hotter terminal and the melting solder acts to cool the standing end of the cable slightly so the body of the cable does not get quite so hot and curl back all the insulation..
As soon as the solder forms a drop on the bottom of the terminal and bitter end of the cable (completely closing off the ends of the strands), pull the heat away and hold the cable very still as the solder chills.
As soon as the solder changes from shiny to mat gray and starts to solidify, take a squirt bottle of plain water and start cooling the lug end clamped in the wood to start drawing heat out of the joint without heat shocking the joint too much by avoiding shooting the water directly on the soldered end of the lug.
Once the joint is cool and dry, clean with a brass brush and alcohol until it is free of soldering flux, and let dry completely.
Paint it with liquid electrical tape, and let it dry.
Slide the heat shrink tubing over the fitting and shrink it.
(you did remember to slide the heat shrink sleeve on the cable a couple feet back so it would not get hot and set while soldering didn't you?)
Paint the end of the cable and the joint ends of the heat shrink tubing with the liquid electrical tape just to be sure it is completely sealed.
If you are really paranoid wrap this with rubber electrical tape or the new self sealing silicone electrical tapes which will self bond into a solid cover after it sets for a while.
Larry
