Many techniques can help locate failing and failed PV modules in a field. However, quantifying module performance relative to warranty thresholds requires measuring the electrical quantities of the modules in question. Simultaneous I-V measurement of all modules in a string is possible, removing irradiance and spectral irradiance as variables in interpreting such measurements that would otherwise be performed sequentially. Performing such measurements without making electrical connection to the individual modules would provide additional benefits of reduced time, risk, and worker hardship. We found that such measurements are possible, but are challenged by inaccuracies involving probing technique and site conditions. Future work to understand the sources of these inaccuracies may enable their mitigation, enabling such measurements to be practical, frequent, and predictive of upcoming module failures.