My mind skipped for a second that the MSD wire is just a relay driver at this point.
But are you trying to drive pumps, fans DIRECTLY, or is this wire just firing relays?
What are you running for a charging system? this point electrically also normally supplies regulator / alternator field. Having voltage drop problems at this point will cause overcharge (overvoltage)
Now knowing "how" you did this, solder and heat shrink, terminal strips, several ways to approach