72 duster firewall wiring questions ???

Need a little help determining what is what on the firewall of this 72 duster. I am doing away with the factory distributor and I am attempting to locate the wire which will feed the new hei switched 12 volts. I am only getting 7-8 volts on the blue wire which feeds the ceramic resistor on the firewall on the drivers side upper corner. What can be elimintated from the firewall to clean things up?? Also what is the rectangular metal box adjacent to the brake booster?