The invention relates to a downhole measurement sensor assembly for an electrical submersible pump that is housed within a rugged, insulated and durable enclosure. The downhole measurement sensor assembly can be manufactured in accordance with the method described herein. The sensor assembly is configured to be inserted into a windings area of a downhole motor of the electrical submersible pump. The sensor assembly includes insulated lead wires that are connected to a thin-film temperature sensing element for monitoring the ESP motor operating temperature. The thin-film sensing element includes thin lead wires that are electrically connected via a connection substrate to the insulated lead wires. The thin-film sensing element is mounted the connection member, and the connection member may include attachment apertures for connecting the insulated lead wires.