I don't think Yamaha Motor is producing any large trucks. They do a lot of things but mostly motorcycles, atv, boat engine, even car engines but not the whole car.
Also, you should note that Yamaha Corporation, the musical instrument maker and Yamaha Motor are now 2 distinct independent companies, even if were originally part of the same group.
They are independent yes, but originally the motor company was an affiliate spin-off. They do have an agreement and share the same logo, and Yamaha Corporation has some shares in the Motor one tho.
a former keiretsu?
Former, current, reformed keiretsu?
> but not the whole car
They actually made at least one model, of which only 3 prototypes were built before the project was cancelled due to the economic situation at the time: the Yamaha OX99-11 supercar was using a detuned version of their formula one v12 engine when they switched to v10. I guess they had built to many of them?