Is the work of an engineer who installs television sets in waiting rooms, as part of industrial projects, considered Haram (religiously forbidden), given that the customer is the one who operates and selects the channels?

The fundamental principle for anything that can be used for both lawful and unlawful purposes is permissibility, unless its use for unlawful purposes is overwhelmingly probable. If the television is predominantly used for permissible matters, such as news broadcasts free from religious prohibitions, then there is no harm in installing it. However, if its use for forbidden matters is predominant, then it is not permissible to install it, nor to assist in its installation; as Allah Almighty says: "And do not cooperate in sin and aggression." If the questioner is able to distance himself from installing a television and similar forbidden things, then there is no harm for him to remain in his job, even if the institution carries out such activities.