An electrical connection assembly of a medical device includes a plurality of electrical contact blocks and a sealing member, which are held within a cavity of a base of the assembly. The sealing member includes a plurality of openings, at least one interior surface surrounding a bore and at least one void. Each electrical contact block extends into a corresponding opening of the sealing member, and a conductive sidewall of each block defines a portion of a perimeter of an area for receiving a lead connector, while the bore of the sealing member forms another portion of the perimeter of the area. The at least one void provides a compressible space in a bulk volume of the sealing member. When the lead is inserted within the area, and a cap is engaged with the base, the at least one interior surface of the sealing member is compressed about the lead.