Suspect Firewall connection block.

I am trying to install an MSD ready-to-run distributor and ignition wires on my 67 Barracuda. Before installing it though I ran some voltage tests. My battery puts out 12.6 volts, a wire off the ignition switch fuse is only returning 10.5 volts back to the engine compartment. The coil positive terminal only read 4.6 volts (after the ballast resistor.) I've inspected the firewall connector block tried to clean the individual terminals, but that'e not helped much. Does anyone make a replacement firewall connection block? Is there an after-market connection black that would work? Before I bother installing the MSD system, I've got to get better, more consistent voltage into the dash and back out to the engine compartment.