1/8 npt is actually 3/8-27.british standard pipe is 3/8-28.like i said,you can buy an adapter so you can use a 1/8 npt sender on your goldwing.i put one on my 1100 years ago but i dont recall the manufacturer.it may have been plews-edelman.
the exact thread size is 3/8-28.its british standard thread.you can buy an adapter fron the bsp to npt thread so you can use a npt sender.btw,the npt thread is 3/8-27