I have an older 68 single field alternator, I need a dual field alternator to tie into my newer dual resistor/electronic VR harness. I understand 71 model year had the older case alternator but added a 2nd field terminal, then went to the squareback alternator the next year (71 1/2). Does anyone have the procedure to add a 2nd field terminal ($3.00 brush?) to the older round backed alternators? Do you unscrew the ground lug and replace with a brush? Several websites reference the ability to do this but none seem to walk you through it. I dont want to buy a squareback dual field, I already have one, but I just want to convert the older one to dual field (reason: its polished!) I took the brushes out of the dual field and one is straight and one is a 90 degree type, which one to buy for the added one or is it different? Thanks.