I'm wrapping up a full rewire using the Classic Update harness from American Autowire. My tach (which was working perfectly before the wire) is dead. Using my multimeter, I am getting pretty constant 12V to the Coil lead and nothing on the 12V lead. My ignition system is an MSD HEI, 6AL box with a tech filter. Any tips or tricks on where I can start trouble shooting this one? Would love to get her running for the weekend.