You didn't specify which engine you have. In 1966, Thunderbirds came with a 390 as the standard engine, with an option for a 428. Either way, the firing order should be stamped on the intake manifold in the vicinity of the carburetor. Assuming you've got an original motor, the firing order should be as follows: 1,5,4,2,6,3,7,8.
ford didn't put a 4.7l in a ford t bird the firing order for a 4.6L that they did use is 1,3,7,2,6,5,4,8
Call Kragens or Auto Zone and they will give you the firing order for any car.
Click the link.
older fords have firing order cast into the intake manifold around calibrator
Firing Order: 1-5-4-2-6-3-7-8
What year, what engine?
Firing order on the 4.6L is 1-3-7-2-6-5-4-8
The firing order is 1-4-2-5-3-6 in the clockwise direction.
According to the 1956 Thunderbird manual the 6 cyl. is a 223 cu. in THE firing order is 1-5-3-6-2-4
Firing order is 1, 3, 7, 2, 6, 5, 4, 8
firing order 97 t-bird, 1-3-7-2-6-5-4-8
Not fast enough