Re: Wiring harness for testing different pickups quickly
I do all my soldering with a pretty cheap 25W iron that I got at a hardware store. I should invest in a more "pro" iron but up to now my cheapo has served me fine. To "hold things in place", I just move stuff out of the way by hand and then use a pair of very long, fine tip tweezers to hold the wires in place to where I'm soldering them. Here's a couple tips that have worked well for me:
1. Strip all the ends first, twist them together if necessary (ex: white+ black and green+bare on DiMarzio) and then "tin" the wires. Heat up the wire with the iron and then melt some solder onto it.
2. Use the finest solder you can find. It melts easier.
3. In addition to tinning the wires, make sure the place you're soldering them to has plenty of solder. In other words, you don't want to be adding solder to the joint when you're holding the wire there. You want as much as you need to begin with.
4. Plug in the iron only when you're totally ready to go. Start soldering as soon as the iron gets hot enough to work. This prevents things from getting too hot and possibly damaging things. If I do a couple things and then there's a break before more soldering, I'll unplug the iron in between.
About the harness to test pickups, I've been thinking about that myself. The main tool you need is a good multimeter. The two main things you're testing are DC resistance and output. You don't need the pickup in the guitar to test resistance. I'm not sure how output is tested, but this is an idea I had (assume DiMarzio colors).
1. Install the pickup in the guitar.
2. Twist together white/black and green/bare.
3. Leave white/black floating and attach green/bare to negative on meter.
4. Attach red to positive on meter.
5. Strum guitar and check output in mA.