In vehicle durability, the determination of accurate input forces can lead to a greater reliance on numerical simulations using analytical models and reduce the need for more expensive and time consuming experimental testing. Traditionally, the input forces are directly measured using load cells. However, in many instances, the direct measurement of force by load cells is either impossible or inaccurate, such as in the case of vehicle body and engine mount loads. To improve the techniques on automobile durability analysis, there is a need to be able to construct the input forces indirectly; i.e., to calculate the input forces by measuring the subsequent structural responses. In essence, the instrumented structure becomes its own load cell. The current study attempts to calculate the body mount loads of a light truck vehicle using the proposed technique. A finite element model of a vehicle body structure is used to locate the areas of load sensitivity. Optimization tools help us direct the placement of strain gages on those areas. When strain data are obtained, this method uses the model to back calculate what the load inputs must be to yield the measured responses. The calculated forces are compared with the direct measurement of body mount loads. The results show good correlation.