For being so simple, DC wiring can get confusing. I'm an electronics tech, so I'm familiar with wiring. Normally, like in your car, red is positive 12 volts and black is negative (ground). EXCEPT on my 69 VW, where red is +12V unswitched, black is +12V switched (hot when the ignition is on), and BROWN is ground. Now I find on my Coleman/Fleetwood PUP that BLACK is +12V and white is ground, except for the output of the 12V converter, which is are blue wires. My head is about to explode.