Hey guys,
Hopefully this will be an easy question.... as I am a newbie to car repair. I let my car sit for one month while on a trip and came back to find it would not start. The battery is only 2 months old. I jumped the car and the minute I removed the jumper cables the volvo died. This should be an obvious alternator issue. Before replacing the alternator I took a closer look and noticed a red/yellow cable laying unattached next to the alternator ( see attached image )
What is the purpose of this wire and if it is necessary, where does it reconnect? Thanks!

 

Do you have a small single wire on the back of the Alt.?
If not that one goes there. That is the trigger to start the Alt. charging.