Hi Rick,
I've attached the questions you asked in the intro thread and will answer them here. It makes the most sense I think.
1) Is there a replacement solderless, easy to install harness for the athearn?I haven't seen one recently. To be honest, it is not that hard to hardwire a harness in on the old BB locomotives. It will take a while the first one or two times, but after that it gets quick and easy. A cheap soldering iron from Harbor Freight is an easy way to get started.
2) Is the current draw too high with blue box athearn?The current draw can be very high, but still within limits for Railpro. There are easy ways to tune these locomotives to run better.
3) Any easy way to decrease current draw on athearn (if it is a concern)?You can run an eraser over the commutator to polish it and remove any burs. Careful filing of the gears will remove burs as well. Replacing the wheels with ones from Northwest Shortline is one of the best upgrades you can do. There are many guides on the internet that are easy to find that walk you through tuning an old BB.
4) Any thoughts on how to convert the Proto2000?Proto 2000 will typically run better than the old BB. You will likely need to replace the axle gears though because they break more often on Proto than on BB from what I've seen. Besides that they have more weight and better detail.
My first Railpro install was a very old early 90's Athearn Blue Box GP50. It was one of my first locomotives from when I was a kid. I did some tuning on it and hardwired in a 9-pin harness, then installed a Railpro module and a speaker. It draws high (700mAh) but runs very smooth and quietly.
This was also my first detail and weathering job on a locomotive.
So in the end it is definitely possible. It is a little more work. Newer locomotives are easier because many have a 9-pin plug already in there.
-Kevin