B+ is the positive post of the battery.

Some GM alternators are 1-wire units, which require excitatation of the alternator field for the alternator to begin to produce power. That 12v excitation voltage is provided to the alternator through the "Ignition" terminal on those isolator models designed to work with this type of alternator.

From your description, I'd say you need the one with the "Ignition" connection, but check the type of alternator you have and see if it's a "CS" type.

Frank

'89 [color:"white"]G-Raider[color:"white"] [color:"black"]Supercharged 3.0L, MegaSquirt 2, lockup A/T, 2.5" exhaust, 172k, Cibie H4s/Oscar SCs, Hella Micro DE fogs, Cobra CB, Superwinch hubs, LSD rear/Aussie Locker front, Bilsteins, Lifeline AGM, Rust-Oleum