On Monday, six teams of chimneys saw the 141,702 square meters in Bridgend, adding firefighters from as far away as Cardiff and Pontypool.
The South Wales Fire and Rescue Service says it appears to be in a complex in the main building and not in it.
The 40-year-old Ford plant is expected to do so in the fall of this year with the loss of 1,700 jobs.
Firefighters said they were called to construction at 19:45 BST on Monday and South Wales police said at 8:20 p.m. that “the chimney was under control.”
Teams from Bridgend, Porthcawl, Kenfig Hill, Pencoed, New Inn and Whitchurch were present.