The phrase "a second major factor" is correct and usable in written English.
It can be used when discussing multiple important elements or reasons contributing to a particular situation or outcome.
Example: "In addition to the economic downturn, a second major factor influencing the market is consumer confidence."
Alternatives: "another significant element" or "a further key factor".
Resolution — the sharpness of the picture — is a second major factor for buyers.
A second major factor which helped to set the stage for the Sigma program involved the strained relationships between different departments and levels within the plant.
Together with improved conductivity, this is likely a second major factor in reduced Rseries and improved performance in our devices compared with previously published studies typically with Cu2S, which is a semiconductor.
A second major factor accounting for high health spending per capita in the United States is the significantly higher prices Americans pay for virtually all health care services and products.
A second major factor cited by Hill was human ignorance regarding the consequences of mismanagement (McGovern et al. 1988).
A second major factor shaping ECEC policies at present is the so-called "welfare reform" legislation of 1996, and the provisions of the new public assistance legislation for poor lone mothers and children.
In this research, the processing methods for each predictand were considered as a fourth major factor in model selection.
A third major factor dramatically increasing the resulting deficits under Obamacare is that the tax increases won't raise nearly the revenues that CBO projects.
The second major factor was the resistance from the regular army, who made it clear that they were willing to act against the elite presidential guard.
The second major factor that determines our ability to sustain attention and maintain peak cognitive performance has to do with the total amount of sleep you manage to get over several days.
