To start with my 1946 Hudson pickup came to me with 6 volt converted to 12 volt. While adding step down resistors to my fuel gauge and temperature gauge, I was confronted with a "rats nest' of wiring behind the dash, well, while troubleshooting I pulled the large wire connector at the top drivers side of the firewall, ( I may note that all of my lights worked previously to include: headlights, tail lights, turn signals, and stop lights). When pulling the previously mentioned connector, half of the male and or female pins broke off  (I should have left well enough alone), and this is where my troubles began. I cut  all wires associated with this connector and spliced them per the colors of the wires . Now I have headlights, brake lights and turn signals, but NO tai lights. Per the 1946 wire schematic, the headlight switch has a "bullet" connector with yellow wire that goes to the Hi-Lo beam foot switch, a "bullet" connector with red wire that goes to fuse panel, and  a screw in terminal with 2 wires, one of these wires (green/yellow) goes to a rheostat, which I don't have, and a black wire that shows spliced into a white wire into the harness somewhere. Whenever I connect this black wire to any wire associated with what I think are lighting wires the lighting fuse blows. Who ever wired the "rats nest" of wiring at least had all of the lights working, but now my proactiveness has "screwed me. Could the change to 12 volt changed the polarization of some of the harness? Before the question is asked, all bulbs have been replaced to accept 12 volts. It should be noted that with headlight switch on, at the headlight junction block with 6 screws, I have power at the 2 forward sets of 4 screws, but no power at the rearmost set of 2 screws. Hopefully someone out there can help me, it is probably something simple that I am over looking, meanwhile I am buying 30 amp fuses in bulk. Thank you for reading my long winded post, Kevin Morrow 302ninefourthree8197