Help with wiring

So I have another thread about wiring in a front camera and now I have a A/V / electrical question. I am trying to use a DPDT switch to have a backup camera override and a front camera override which is powered via a relay.

Upon wiring everything the switch made both sides of the DPDT switch show only the front camera, when connected with a 12v source. In frustration I forgot to plug in the power wire but had the relay going and I was able to get the switch to so as I asked of it, yet the relay had no power.

Now I dont know if it matters but I was also able to somehow power the camera by only attaching the positive wire to power, didnt need the negative. Can someone help me understand this? Im almost clueless when it comes to electrical components and dont understand how something that requires power is being powered unplugged.