electrical gremlins are back

The voltmeter I am referring to is mounted under my ashtray along with an oil pressure gauge and a water temp gauge. They are I equus brand. When I disconnect the battery, the gauge reads just below the "8" on the meter. When I connect it with the key off, it reads right at 8 so I know something is wrong there. I plan on connecting the voltmeter to the fusebox once I get all of this solved. So currently the positive voltmeter wires is routed through a grommet in the firewall to the bottom post on the voltage regulator. I have 12v there when the key is on when I test that with my multimeter. I tried wiggle testing at the ignition switch, headlight switch, fusebox, and bulkhead and nothing. I'll keep trying that tomorrow. After I soldered the black and red wires from in the cab, out through the bulkhead and to the fusible link, I used my multimeter there and tested 12v. I then heat shrunk it so I can go back and test again, because I'm wondering if it's possibly a bad solder? I'm using butt connectors to connect the 2 big red and black wires at the bulkhead and when slipping my multimeter in there, I get .2v. I'll go back and take the butt connector off for a more accurate answer however. As far as the bulkhead connectors, nothing was melted or heavy corrosion so I wire brushed the terminals and sprayed them with compressed air. I cut back some of the factory tape around the wiring to get to the welded splice which when I put my multimeter on there, I got .2v also!!! I know this isn't rocket science and this is driving me crazy not figuring it out!