About alternators...when the key is the run or start position and the engine isn't running your alternator light and your brake light are both on, if you have access to the wiring diagrams, here's how it works. The brake light is only supposed to be on when either your emergency brake is on or your fluid is low in the master cylinder...so what's going on? The alternator light is fed from the brake light circuit through a diode to the alternator. When the alternator isn't charging it is a dead short to ground, so the brake light and the alternator both light up. The alternator requires an exciter voltage/current in order to start charging, this is provided by means of this alt/brake light circuit which is fed from the 15A engine fuse. Once the engine is started and the alternator is turning because it is excited it will start charging against the feed from the alt/brake light circuit, but because there is a diode in the circuit, the alt cannot back feed this circuit and because the alt is now charging there is no path to ground for the alt/ brake light circuit and the lights go out.