In this work, a computationally-efficient modeling approach is developed to predict the electromagnetic noise induced in the terminal units of random bundles of twisted-wire pairs mounted onboard spacecraft. The proposed model combines the results of a preliminary fullwave simulation, aimed at evaluating the electromagnetic field inside the space vehicle's metallic body, with a stochastic model of a random bundle, based on multiconductor transmission line (MTL) theory. Model assessment versus measurement data obtained characterizing real wiring harness in a full-scale satellite mock-up demonstrates the large sensitivity (up to 40 decibels) of the induced noise levels to different bundle configurations, and corroborates the effectiveness of the proposed simplified modeling strategy for estimating the modal noise voltages induced in the terminal units.