Abstract: A tool for installing an O-ring in an inwardly facing O-ring groove in an ectrical connection includes a guide shaft and a contact member slidably and rotatably received in the guide shaft. The guide shaft includes an elongated cylindrical shaft portion and a flared end portion on the shaft portion. The contact member includes an attachment portion for slidably and rotatably securing the contact member on the shaft portion and a contact finger on the attachment portion which extends in a direction toward the flared end portion of the guide shaft. The tool is operable by assembling an O-ring on the shaft portion between the flared end portion and the contact finger, inserting the flared end portion into a connection and then manipulating the contact member to advance the O-ring into an O-ring groove in the connector with the contact finger.