There is a simple test to also try. If your truck has the moulded plug ( 4 wire) off the regulator, pull the plug off while the truck is running. Take a piece of heavy guage wire, about 6 inches and strip off both ends. Take the wire and jump the first and third wire. If you look at the plug, there's 3 wires spaced evenly apart and one a little farther apart. Jump the first and third wires of that group of 3. if the alt. is good, the RPM's will drop and the alternator will start to whine. That jumps it to full output. if it doesn't, the regulator is bad. As described before, the fusible link is right off the starter solenoid. It is usually within 6 inches of the solenoid. They are usually imprinted with the guage on the rubber block, say "14" or "16". Some of the early 60's cars and trucks had just a piece of wire that looked just like the others, except it has a softer feel to the insulation. Sort of a spongy feel to it. If you find it and it's bad, make sure you replace the same exact length as you remove or it will create resistance and burn out again. When you jump the regulator with the wire, have someone pull the battery cables and check the voltage across them. If you have been checking the voltage with the cables attached and putting the leads on the battery posts, you may be getting the "surface charge" reading which is usually 12.8 volts.

 

While unplugging the battery from the truck while its running is fairly safe with a generator, it is a different story with an alternator. It truth, it really isn't safe with either. The battery is essential in regulating your voltage output from the generator/alternator. It serves as a reference point for the voltage regulator, thus allowing it to hold the voltage down around 14v or so. When the battery is removed, there is no longer a reference point for the regulator or alt/gen and the voltage can spike to tremendous levels. (from 12v to the 100s of volts) This spike may only last for a few seconds, but it is extremely dangerous.

The best thing to do when your having charging system problems is to buy a wiring diagram from this site and trace every wire. More than likely, you'll find that someone in the past has bypassed something in the harness trying to get the thing running. If you have a voltmeter or ammeter in the dash, these are commonly bypassed, or wired incorrectly.

I personally would check all frame/motor grounds and ensure they are clean, and free of corosion. A bad ground can cause all kinds of gremlins to show up.

Good Luck

Tyson