Mental representations of target features (attentional templates) control the selection of candidate target objects in visual search. The question where templates are maintained remains controversial. We employed the N2pc component as an electrophysiological marker of template-guided target selection to investigate whether and under which conditions templates are held in visual working memory (vWM). In two experiments, participants memorized one or four shapes (low vs. high vWM load) before either being tested on their memory or performing a visual search task. When targets were defined by one of two possible colors (e.g., red or green), target N2pcs were delayed with high vWM load. This suggests that the maintenance of multiple shapes in vWM interfered with the activation of color-specific search templates, supporting the hypothesis that these templates are held in vWM. This was the case despite participants always searching for the same two target colors. In contrast, the speed of target selection in a task where a single target color remained relevant throughout was unaffected by concurrent load, indicating that a constant search template for a single feature may be maintained outside vWM in a different store. In addition, early visual N1 components to search and memory test displays were attenuated under high load, suggesting a competition between external and internal attention. The size of this attenuation predicted individual vWM performance. These results provide new electrophysiological evidence for impairment of top–down attentional control mechanisms by high vWM load, demonstrating that vWM is involved in the guidance of attentional target selection during search.