Thermoking ts-500 box truck blows starter fuse

[Socaltech]

Customer has a TK ts-500 that blew the starter fuse, put a new fuse in and it ran for a day and blew the fuse again, any ideas what could be blowing the fuse?

[cadwaladr]

Faulty start relate,faulty starter or the wire rubbed through close to the starter

[cadwaladr]

Faulty start relay