I bought a generic DC power extension cable and I'm trying to wire it to a connector with a cable attached. The connectors cable clearly has two wires - a red and black/+ and -. This is what I'm used to, coming from the world of breakout boards and tiny wires. The generic wire, once stripped, however has outer bare wire strands surrounding a sheathed tiny wire:
(I've attached a photo. I've twisted up the outer wire so I could test it with my multimeter). My logical assumption is that the inner sheathed wire is + and the outer is -. Is this correct? I've hooked it up to my solar panel and tested it on my multimeter. It shows 7v when I've got the red wired touching the inner sheathed wire and the black wire touching the outer, and -7v the other way round. I just don't want to connect it up and fry my solar charger board. It's be great if someone could give me a 'yes! you're right!' confirmation please?