VLS's lighting products offer enhanced brightness along with intelligent features and sustainable solutions to decrease CO₂ emissions. These new features ensure an optimal driving experience, prioritizing safety and comfort for both drivers and pedestrians. The reliability of the electronic systems is confirmed through standard tests like power cycling or thermal cycling. VLS is also working on simulation solutions to numerically validate the design and reliability of these electronic systems. A cause of failure in thermal shock tests is the thermal fatigue of solder joints, resulting from repeated thermal stresses on the assembly caused by the mismatch in Coefficient of Thermal Expansion (CTE) between the LED and the substrate. The primary focus has been on developing a predictive simulation method to assess the reliability of LED assemblies under combined power and thermal cycling. In this study, we delineate the steps involved in validating the simulation of combined power and thermal cycles in LED systems. Using thermomechanical simulations, we examine the cumulative damage to solder joints caused by both thermal cycling and power cycling. In a combined power thermal cycling test, the electronic system experiences a combination of high cycle fatigue (HCL) due to power cycling (several million cycles) and low fatigue damage (LCF) from thermal cycles. In order to consider the combined fatigue damages due to those two loadings a new approach was considered. Firstly, we will begin by analyzing the spatial and temporal evolution of temperature within the assembly through transient thermal simulations. Subsequently, based on these temperature variations, we conduct a decomposition of damage analysis between HCF and LFC models, examining them independently. The Low cycle fatigue model was validated by comparing the fatigue life prediction with results from thermal cycle testing. Following this, we assessed the cumulative damage of HCL and LCF by comparing it with outcomes from combined power thermal cycle testing. Finally, we establish a correlation between the experimental number of cycles at failure and the cracked surface observed with dye penetrant to evaluate the accuracy of our model's assumptions. This new method demonstrates promising predictive capability for combined power thermal cycle testing results, while also enhancing our understanding of design parameters that accelerate failures.