Thank you very much and thanks for taking your time to play our game and comment on it :D
The pulse signal attack is supposed to work where the lit up part of the wire is what damages the enemies if it touches them, and on top of that the two characters need to pass it back and forth, so first the blue guy (Sig) can pulse, signified by the blue coloured wire, and then once it's reached the other end, the purple guy (Null) can pulse, now signified by the wire being purple. There was going to be a HUD element that shows which side could pulse when but we lost that work in the final moments sadly.
Also it could be purely possible you've found a bug if you already knew and understood the above, as we did at one point encounter the possibility of neither Sig or Null able to pulse for some strange reason, we did think we had fixed that however.
-Scott