As the technology gets upgraded every day, automotive manufacturers are also paying more attention towards delivering a highly reliable product which performs its intended function throughout its useful life without any failure. To develop a reliable product, functional and durability testing is not only sufficient rather it should undergo various types of stresses at different levels, to identify its potential modes of failure. By reliability testing, most of the failure modes of a component can be analyzed and eliminated in the design stage itself, prior to production. In this paper, electrical relay of a commercial vehicle was taken up for study to analyze the causes for field failure and to estimate its reliable life in the customer operating conditions. Few of the field failure samples were tested for its performance characteristics with typical testing protocol and strip out experiment was carried out to analyze the various failure modes. Data acquired at customer operating conditions to ascertain different stress levels i.e. Load, vibration and temperature. To conduct reliability test, new samples were taken up from various manufacturing plants, as it is more realistic than getting the samples directly from suppliers. Operational and destructive limits of relay samples at each stress levels were found by step stressing. Reliability test was performed with combination of various stresses at different levels within their destructive limits. Failure modes as in field condition were simulated and failure causes were assessed. With the results of reliability testing, the reliable life of electrical relay was estimated under customer operating conditions.