Final answer:
Neither Technician A nor Technician B is entirely correct; the starter main circuit does include a fuse, relay, and switches, which Technician A correctly identifies, but there is typically a ground connection to the chassis for the starter, as per Technician B's description, ensuring a complete circuit.
Step-by-step explanation:
Both Technician A and Technician B have correct and incorrect statements regarding the starter main circuit. Technician A is correct in stating that the starter main circuit generally includes a fuse, relay, and switches. These components are part of the control circuit that actuates the starter. However, Technician A is incorrect in saying that the main circuit does not have a ground wire. In fact, the starter main circuit does require a return path to complete the circuit, which is typically accomplished through a ground connection to the chassis, but this is not the same as having no ground wire at all.
Technician B's assertion that the circuit is just a positive battery cable to the starter and uses the starter's case for the chassis ground through the case of the starter is also partially true. This is a common method of grounding in automotive electrical systems, where the metal body/frame of the vehicle serves as a ground plane or return path for electrical circuits. Still, there typically has to be some form of ground wire or strap that physically connects the starter (or its casing) to the vehicle's chassis to ensure a reliable ground connection.