The "R" terminal on a Delco-Remy alternator is the same as the "D+" terminal on your Bosch or Bosch equivalent. I should not mean "Regulator" because the regulator is built in to the alternator housing - there is no separate regulator and I don't know what the "R" means in Delco-Remy-Speak. Why the hell do the Bosch guys call the +12Volt terminal "30"?? I dunno. They prob'ly have a decent engineer-like reason, like Radio operators signing off with "73 " (Best Regards) or "88" (Love and Kisses). For this episode, "R" = "D+"="Blue Wire".
When you touch the B+ and D+ terminals together with a wire (those two on the top of your alternator) even for just an instant, you momentarily create a magnetic field that remains when you remove the wire because the charge creates that field in a ferrous (iron) core within the alternator which holds that "charge". That magnetic field is what begins to generate a voltage field when the alternator begins to turn. Because the bulb is attached to the D+ and the battery is ALWAYS connected to the B+ terminal, that magnetic field is maintained seemingly forever, unless the battery is disconnected for a looooooooooong period of time, which then sometimes allows the magnetic field to collapse (actually, it dissipates or weakens over time until it is no longer strong enough to generate the state changes inside of the alternator to cause it to generate voltage). Touching those two terminals together, even for an instant, re-institutes that field to allow the alternator to start producing electricity. Even to a lot of seasoned engineers, it is almost like magic.