Enabling System-of-Systems (SoS) security is an important activity when engineering SoS solutions like autonomous vehicles, provided that they are also highly safety-critical. An early analysis of such solutions caters for proper security architecture decisions, preventing potential high impact attacks and ensuring people's safety. However, SoS characteristics such as emergent behavior, makes security decision-making at the architectural level a challenging task. To tackle this challenge, it is essential to first address known vulnerabilities related to each CS, that an adversary may exploit to realize his attacks within the unknown SoS environment. In this paper we investigate how to use Game Theory (GT) approaches to guide the architect in choosing an appropriate security solution. We formulate a game with three players and their corresponding strategies and payoffs. The proposal is illustrated on an autonomous quarry example showing its usefulness in supporting a security architect to choose the the most suitable security strategy.