The starter on a 1990 Nissan pickup is mounted to the transmission housing and can prevent the truck from starting when it goes bad. The starter can be removed and bench tested to ensure it is faulty before spending a lot of money on a replacement starter. The bench test can be done at most automotive parts stores. Most stores sell brand new starters and remanufactured starters. The latter are rebuilt and cost less than a new starter.
Removing the Starter
Open the hood to disconnect the battery. Unbolt the negative and positive cable from the battery with a socket wrench. This will isolate the electrical power from the vehicle.