Adding MSD to 70 Swinger

Hello, First time poster long time lurker...
I have a customers 70 340 swinger in my shop being reassembled from a total restoration. My question is this: We are running a MSD distributor that requires 12v. I have 3 wires at the ballast resistor, blue and brown on one terminal and a blue on the other terminal. My thoughts were to tie the 2 blues together, but whats up with the brown?

Thanks...Pete