The Third Cybertron War is a conflict between the Autobots and the Decepticons that occurred some time prior to the earth year 1985, apparently in the distant past. It should not be confused with the Third Cybertronian War.
The Decepticon drone Deceptitran uses encryption quite similar to the Decepticon transmissions of this period, and it's possible he dates from this time, though his occupation of the Tlakakans planet seems to be of a much more recent vintage.
Generation One cartoon
Perceptor intercepted Deceptitran's call encrypted for assistance and was able to discern its overall intent even without decrypting it. It was only later as he, Cosmos, Bumblebee and Seaspray were heading toward the Tlakakans planet that he found a strikingly similar transmission in his memory banks from the Third Cybertron War that he realized they were actually answering a Decepticon distress call!
- It is unclear in context whether Perceptor's reference to his memory banks means this was a transmission he has personally encountered long ago, or an even older one he simply had record of. As a result the period of the Third Cybertron War remains completely unknown.
- In Five Faces of Darkness, Part 4, the ghost of Optimus Prime (inside the Matrix) reveals the nature of the Third Cybertronian War to Rodimus Prime. That war must be different from the Third Cybertron War mentioned here by Perceptor for two reasons.
- Perceptor's mention (in the second season) of the Third Cybertron War suggested it happened the past and is now over. Optimus Prime said the Third Cybertronian War was still going on (in the third season).
- Optimus Prime only revealed the Third Cybertronian War to Rodimus Prime in the third season, along with the First and Second wars, which must have been lost knowledge to present-day Autobots, so Perceptor couldn't have known about the "Third Cybertronian War."