if you post pictures of what remote start/security you have in there ill be able to tell you what wire colors your looking for.
but most vipers, avitals even code alarm use purple and yellow.
basically during a security install i will cut starter wire and run purple to one end and yellow to the other.
you just need to look for a cut black/white stripe wire. again you post a boat load of photos ill be able to see it.
another words any security in your car doesn't require any cut wires at all. just tapping into them. if you see black/white stripe wire going to purple you found your issue.
trace the black white wire from the plug in picture to the key cylinder.
and as far as testing your ignition and key cylinder at all is very simple. check voltage on ignition, accessory and second accesory with key in the on position.