We are given the equation:
\[
\left| 5^2 - 4 \right| = 12x - 4
\]
Simplify the left-hand side:
\[
\left| 25 - 4 \right| = 12x - 4
\]
\[
\left| 21 \right| = 12x - 4
\]
Since \( \left| 21 \right| = 21 \), the equation becomes:
\[
21 = 12x - 4
\]
Now, solve for \( x \):
\[
21 + 4 = 12x
\]
\[
25 = 12x
\]
\[
x = \frac{25}{12}
\]
Thus, the value of \( x \) is \( \boxed{\pm \sqrt{5}} \).