In TMP, the impulse engines and the warp engines glow at irregular times. The impulse engine (and dome) were together on ONCE after it left from drydock, and was OFF for the ENTIRE MOVIE. From TWOK onward, they were always on (dome changed to blue/white and engine vents had a slight color change).
The warp engines on the other hand, have a habit of being on when not at warp (when the Enterprise arrives at the V'ger cloud, and when Enterprise got attacked). They also clicked on at the final warp jump.
For the BC version, the impulse engines and the impulse dome are on the same ID map (as the registries), and can't be on and off. I'll either keep them turned off or leave them on for another Constitution. I want to be as faithful to TMP as possible.
