Voyager 1 post-heliopause telemetry (2012–2025) is analyzed for covariation between the radioisotope thermoelectric generator (RTG) electrical power deficit and inferred interstellar electron density from Plasma Wave Subsystem (PWS) plasma-frequency measurements. After controlling for mission time/heliocentric distance and applying heteroskedasticity-and-autocorrelation-consistent (HAC; Newey–West) standard errors, the association remains significant (t = 5.51, p = 1 × 10−4). A first-difference test on annual changes yields r = 0.74 (p = 0.004). Stringent phase-randomized surrogates give borderline significance (p = 0.058), and the relationship is regime-dependent (2012–2020: r = 0.993; 2021–2025: r = −0.587). A characteristic length scale L0 ≈ 11–43 astronomical units (AU) is obtained by three estimation procedures. These findings were originally motivated by predictions from the QuEST framework, which proposes that physical measurements couple to local spacetime structure. However, all results are derived independently of any theoretical assumptions.