Electron paramagnetic resonance (EPR) has been employed to examine thermo- and photo-activated interactions between as-grown intrinsic defects and nitrogen/boron impurities in nominally high-resistivity 4H SiC produced without intentional vanadium doping. The EPR spectra, recorded in the dark at 4 K, revealed either a low concentration of paramagnetic boron, nitrogen, or a carbon-vacancy-related defect (ID-1). The photo-induced charge transfer between ID-1 and both boron and nitrogen has been detected. In some samples, illumination with 0.9-1.6-eV light at 4.2 K quenched the ID-1 signal and produced an approximately equal amount of shallow paramagnetic boron. Exposure to 1.9-2.7-eV light restored the ID-1 center and produced shallow paramagnetic nitrogen. A model based on excitation from the band edges and the threshold energies obtained from the photo-EPR data placed the ID-1 level 0.9 × 0.1 eV above the valence-band edge. Comparison of these data with that obtained from other samples that exhibited excess boron or nitrogen impurities suggested the presence of an additional defect no more than 0.9 eV below the conduction-band edge. This defect can exchange charge with the nitrogen donor.