I have a 8 speaker system. The doors have 3 each. A 6.5, a 3.5, and a tweeter. The 6.5 and 3.5 are connected by 2 wires. Black and red. Now, the plug goes to the 6.5 and it has 4 wires. I changed the 6.5's but I needed to bypass the plug. I simply tapped into the wires using a diagram found on the web. But the diagram only showed a 6.5 and a tweeter. No 3.5 speaker. Which wires are + and - on the plug?