The invention relates to a cable joint testing device for vehicle lights, which comprises an insulated support, a clamping tongue and a cylinder, and is characterized in that the insulated support comprises a pedestal at the lower portion and an inserting groove at the upper portion, at least two groups of control pin assemblies are arranged on the insulated support, fixing rods of the control pin assemblies are installed on the insulated support, a lower portion of each fixing rod is connected with a power supply, an upper side of each fixing rod is positioned in the inserting groove, and a movable rod is inserted into a shaft hole of the fixing rod and abutted against a spring seat of the fixing rod through an ejection spring; the cylinder is installed at one side of the insulated support, and a movable side of the cylinder is connected with the spring seat; the clamping tongue is disposed in a clamping tongue groove of the spring seat, a protruding portion of the clamping tongue penetrates out of the spring seat, and the protruding portion of the clamping tongue in a free state is positioned at one side of the inserting groove; springs are disposed in the clamping tongue groove in the spring seat; blocking shoulders of the clamping tongue are corresponding to limiting blocks of the spring seat; and a cover plate is installed on the spring seat and blocks the clamping tongue groove. The cable joint testing device is low in manufacturing cost and using cost and is convenient and efficient in operation, and a cable joint can be automatically ejected after being tested.