Definitely the way to roll. Centech makes a great harness for these that is pretty easy to install. There arent alot of extra circuits for lots of extra stuff, but there are enough...and personally, most aftermarket stuff I run, I use a direct line from the battery (or additional junction box) and use relays and in-line fuses. There are other wiring harness options, but the Centech is a nice piece at a reasonable price-point. You can do a search on them (above) and find some additional info, upgrades, etc. I added several more weather-pak connectors to mine and used them throughout the truck. Everything becomes a bit more modular and when you need to do maintenance, tear into something or upgrade some other piece, you dont have to hack up the wiring, just disconnect the connector and wire your new connector up for your additional piece or upgrade.
As far as the motor, I agree with the others. Find out whats wrong first, get it on the road if possible and begin the "bonding" process before you start to get too many ideas about what you think you want/need. Chances are good that your ignition system or carb may need some work. I dont recall what year they started putting in the Ford Duraspark II, but its a good, dependable ignition system that you can find parts for anywhere...so that would be something to consider if yours still has points...guessing that it may already be electronic ignition though.
Rebuilding the carb is pretty easy to do. As these things sit, the fuel turns to crap, so you may have junk gas in the tank...and in the carb. So, cleaning both may be a good idea. It may take a couple of days to go through and get everything tuned up, tightened and the fluids changed--all of them--just a good idea and its a great introduction to the vehicle. The Haynes and CHiltons manuals are both handy and can be picked up on Amazon (older Haynes covers just Broncos, whereas newer one covers multi years of truck and Broncos) or at your local autoparts store...if they dont have them in stock, they can get them within a couple of days.
NOW, IF you find out that there really are motor problems. Then consider finding a late model 5.0 (with EFI) and make the jump to fuel injection. For Explorers and Merc Mountaineers are good choices, Town cars and Crown vics can also still be found with low mileage. Mustangs, are the obvious choice, but many have high miles on the motor...but would make a great canditate for a rebuild and donor (of just about everything). As well, you COULD buy just baout everything aftermarket and spend alot of money. Finding a donor is a good idea. However, you can get the engine harness through FMS and several other vendors sell aftermarket EFI harnesses or rebuild stock harness (removing uncessary stuff and upgrading). This is a great upgrade....not something you have to do, but the truck will run better, burn cleaner and get better mileage, which will be pretty miserable by the way...in case you didnt know, the Bronco was not endowed with optimal aerodynamics...but they are pretty freakin awesome and a whole lot of fun!
Good luck and have fun.
John
