Well, I do stuff like this for a living, and been doing it for many many years.
Lets consider the soldering part first.
I am
very good at soldering.
I have to be. I have had to save multilevel boards worth thousands.
I have soldered with soldering stations that cost several hundred dollars, and with a nail heated with a torch.
The station was easier.
I have run into a lot of misconceptions about soldering irons. Back when solid state stuff first started coming out, low wattage irons were what you absolutely
had to have to keep from burning the small parts up.
As a result, lots of parts got burned up with low wattage soldering irons.
As it turned out, the trick was not to put a small amount of heat and capacity onto the part, the correct way was to put a lot of heat and capacity onto the part to get the joint soldered fast before the heat had time to spread.
Which is why the Weller system is the best. And what makes it so good for electronic stuff, makes it ideal for what you are doing.
I have a couple of this station.
http://www.testequipmentdepot.com/weller/solder/wtcpt.htm
Its great for me, but you might be better off served with this one.
http://www.testequipmentdepot.com/weller/popups/tcp12p.htm
I have one of them also, and it works very well.
The secret to their success is that they have a large heat source combined with a thermostat.
The low wattage irons never get over a certain temp due to the fact that the heating element can only get it so hot before it starts radiating as much heat out as it can produce.
But, when you touch the tip to a heavy piece of copper, it sucks the heat out faster than the element can replace it, and you get a bad solder joint.
If you put in a big element, it gets the tip too hot and burns up the solder.
Weller has a big element that is cycled by a magnet in the tip. When it reaches the set temp, the magnet loses its strength and a spring breaks the contacts turning off the element.
When it cools, it turns back on.
When you touch the tip to some heavy copper, it kicks the big element back on and maintains the heat.
A good iron makes all the difference in the world.
For general use under the hood soldering the heavier wires, also consider this gun.
http://www.testequipmentdepot.com/weller/solderandheatguns/d650.htm
Its the upgraded version of the old Weller 550. Its able to pump lots of heat into a heavy joint.
And would probably do about 85% of everything you needed done on a Blazer.
Next is the solder.
I use Sav-a-bit Mulicore exclusively. Unfortunately you cannot buy it any more. I bought up the last a big catalog company had several years ago, and I should have a lifetime supply.
The flux in the solder is critical. It comes in different amounts of reactivity. Too little, and it will not clean the joint well enough for the solder to bond.
Too much, and it will corrode afterwards.
Here is a long thread about soldering and fluxes.
coloradok5.com/forums/showthread.php?t=287947
Just in case you did not know, NEVER use acid core solder. If you accidentally do, cut out at least 4 to 6 inches of the wire past the joint, or that much past the green crud if you found it late, and throw away the soldering iron tip you used.
Also, you almost must use 60/40 lead/tin solder. Never 50/50. That is for soldering radiators and copper pipes.
Plus, you need to start looking for real lead solder. Its getting harder and harder to find as the nanny state bans it.
Its still the best for what you want to do.
If you have to use the new government approved lead free solder, it will work, but its an unnecessary hindrance.
Now, a quick mention of crimp connectors.
Properly done a crimp connector is as good as, or even superior to, a soldered connection.
I know, I had a hard time believing it myself. A proper crimp, will actually displace the surface film of the wire and the crimp and make an airtight bond.
I have seen the data, and I'm convinced.
But, I still solder most of my connections.
Mainly because you need expensive, controlled force crimpers, and high quality connectors to make it work.
A good setup will not only crimp the connector to the wire, but there is a second crimp that clamps down on the insulation to provide strain relief and mechanical strength.
In high vibration areas like boats, they do not recommend soldered joints. Because the solder soaks into the wire, and makes it stiff and hard.
Then, where it stops, the wire is suddenly flexible again and that creates a stress riser that can cause the wire to break at that point.
As far as heat shrink is concerned, except for places in the engine compartment real close to heat, use the adhesive lined heat shrink.
It has some hot melt glue inside the tube. It melts slightly before the tube starts to shrink. Then, when it shrinks, it gets squeezed into all the parts of the joint and out the ends.
Then it hardens but stays a little flexible.
This makes the joint both water and air tight. Stopping corrosion in its tracks.
They also sell crimp fittings with adhesive lined heat shrink insulation. Well worth the cost.
You crimp the joint, then heat it and its sealed. Saves a step.
They also sell adhesive lined, heat shrink insulated, solder inside, butt splices.
You crimp the splice, heat it, and the solder melts inside and solders the joint while the heat-shrink seals it.
Expensive and hard to find, but neat.
I may post some more ideas later, and I will try to find some links to those types of connectors and heat shrink.
I've been meaning to ask you how you got into it. Perhaps a PM conversation will ensue. 
I'm considering the possibility of pursuing that kind of work in addition to, or after, my MFA degree.
Thanks. 
I kinda gave up on that idea but this was a long time ago. I would love to find these in bulk for a lot less than $2.60 each!
