The 'E' Type Forum

Aloha!

Most 4TR controllers are with 3 pins, others with 4. For what is the fourth for? I enclose pics of two units, the most left connector is marked with B+, the other has A. Are they the same still? Both are NOS-parts.

Oops, I was able to add any pics as a new member or I don't know how to do it.