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In this article, we continue the structural study of factor maps betweeen symbolic dynamical systems and the relative thermodynamic formalism. Here, one is studying a factor map from a shift of finite type $X$ (equipped with a potential function) to a sofic shift $Z$, equipped with a shift-invariant measure $ν$. We study relative equilibrium states, that is shift-invariant measures on $X$ that push forward under the factor map to $ν$ which maximize the relative pressure: the relative entropy plus the integral of $ϕ$. In the non-relative case (where $Z$ is the one point shift and the factor map is trivial), these measures have a very broad range of application: in hyperbolic dynamics, information theory, geometry, Teichmüller theory and elsewhere). Relative equilibrium states have also been shown to arise naturally in some contexts in geometric measure theory as a description of measures achieving the Hausdorff dimension in ambient spaces. Previous articles have identified relative versions of well-known notions of degree appearing in one-dimensional symbolic settings, and established bounds in terms of these on the number of ergodic relative equilibrium states. In this paper, we establish a new connection to multiplicative ergodic theory by relating these factor triples to a cocycle of Ruelle Perron-Frobenius operators, and showing that the principal Lyapunov exponent of this cocycle is the relative pressure; and the dimension of the leading Oseledets space is equal to the number of measures of relative maximal entropy, counted with a previously-identified concept of multiplicity.