Neural cluster

From Teletraan I: The Transformers Wiki

The neural cluster is the weakest spot on any Transformer, especially one living in the UK comics. Originally its location wasn't pinned down, but a letter column confirmed that it was on the back of the neck. Death's Head once figured that a direct hit to this spot would take out even Galvatron. Unsurprisingly, Galvatron decided to beat the slag out of him rather than let him test this theory. Fire on High!