Wow, that IS fishy, but should be easy to resolve. Try measuring the voltage from battery negative to the frame, expecting near zero volts. Then battery negative to battery positive, expecting 12 volts. Then battery negative to the battery end of your red wire going to the black fuse box, expecting 12 v. Then battery negative to the fuse box end of the red wire, expecting 12 volts. Finally, measure battery negative to both sides of Fuse 3 in the black fuse box, expecting 12v. The first unexpected measurement should point to the problem. The ignition switch position shouldn't matter.