He belongs to Cybertron, not any faction, but Impactor pays the price in the end when he takes gunshots to shield Ratchet from the Seekers. Impactor enlists too as he believes in Ratchet but also, he knows Megatron's plan breaks the code he signed up for. Ratchet doesn't belong to any side himself, but Optimus recruits him to help repair a Spacebridge so they can get the Allspark off-planet.
The Decepticon was left for dead by his brethren but when Ratchet nurses him back to health after a building fell on him, he becomes more neutral.
