My truck has sat for a while and when I tried to start it, the battery was dead. I jumped it and it started right up and ran fine. When I removed the jumper cable, it shut right down. I tried it twice to be sure and it shut down both times. Is it my alternator? And if it is the alternator, can I change the brushes in the alternator. And can the brushes be changed without removing the alternator from the truck? Any help is appreciated.
Thx

 

Sundown - first thing to do would be to install a new battery; your truck battery might be so low that the alternator cannot charge so the engine dies.

Once the truck is running (1) check to see if the charging light is now out (2) measure the voltage across the battery terminals and post that.

Do NOT remove a battery cable from the battery once the engine is running - EVER, that "test" is only for old generator-equipped vehicles, will fry an alternator.