Comparing to a relative position.

This should be an easy question, but I'm having trouble with it.

I'm working in a 2D field, with a space ship type game object that is player controlled. There are engines on the side of the ship, and they work fine so far, apart from the controls. See, when the player presses left to rotate the ship left, the engines on the right need to turn on, while the engines on the left stay off, in order to rotate the ship. The deal is, since the ship is player generated, I need to find out which side the engine is on, and since the ship can turn, I can't use world space.

Long story short, how can I find out if this object is on the left or right relative to the ship only?

if (transform.InverseTransformPoint(engineTransform.position).x > 0.0) {
    // right
else {
    // left