He also had me start the truck and disconnect the battery to see if it died. It did not so he said that the alternator is working and supplying power to the truck.
Common misconception. That test is only half right to what most people think. If you pull the battery and it dies, for sure your alternator is shot. (that is where that test is correct to what people think). If you pull the battery and it keeps running, it does not mean your alternator is good, or bad. It means you have to actually put a voltage meter on it and get a reading. Your alternator may be putting out enough voltage to run the engine, but not enough to run the engine and charge the battery and run lights and stereo and ect. So you need to put a full charge on the battery, start the car, and put a volt meter on the battery. You have to look up your factory specs for voltage, but typically it is between 13.4-14.2V.
Also check your ground wires. If your truck has loose ground somewhere, it will get connection one second and then slight shift and it wont, and then it will, and then it wont. So make sure all of your grounds are tight and getting a good connection.
