With the rapid development of new energy vehicles and power electronics industry, the stability and durability of automotive wiring harness connections have become key technical issues. In this paper, a thermal shock test is designed for aging phenomenon caused by extreme temperature conditions of 25 square copper wire harness-terminal connectors in actual use of vehicles. The results show that after 72 thermal shock cycles, the grain organization of copper wire inside connector is significantly refined and the percentage of large-angle grain boundaries is increased. In addition, the distribution of cubic texture orientation {100} <001> weakens and transforms towards the shear texture {111} <111> parallel to the Z direction of common grain organization. In tensile test, the average tensile strength of joints after thermal shock increased by 6.08 %. The resistance of aged joints increased by 14.75 %, but still met the electrical safety standards. The temperature rise of joint resistance increased by 3.81 degrees C after being connected to a constant current of 100A and lasting for 2.5 h. In terms of corrosion resistance, the improvement of joints after thermal shock test is related to microstructural changes in joint material. Grain refinement introduced a high fraction of grain boundaries and more grain boundaries were able to act as barriers to prevent the penetration and diffusion of corrosive media.