<p>This study assesses the impact of resistance spot welding on three-sheet stacks of DP780 advanced high-strength steel, a configuration that remains underexplored despite its growing relevance in automotive body construction. While most prior research has addressed two-sheet welding, the mechanical and metallurgical complexities of multi-sheet joints require further investigation. To address this gap, the effects of pre-heat and post-heat pulse parameters on weld quality were systematically studied. Experimental methods included dynamic contact resistance monitoring, metallographic analysis, microhardness, and tensile-shear testing. The results show that pre-heat pulses improved surface conditions but had limited influence on nugget growth, whereas post-heat pulses contributed to better thermal control during cooling, leading to more uniform nugget formation and enhanced joint strength. Post-pulse welding achieved up to a 6% increase in tensile load and promoted more desirable pull-out failure modes. These findings provide practical guidance for optimizing pulse schedules in multi-sheet resistance spot welding and contribute to the development of stronger and more reliable joints for lightweight automotive structures.</p>