metal brake line caught fire any idea what might have caused this

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Newly rebuilt 5.9l Cummins diesel motor in a 2006 Dodge Ram 2500 - went for test drive and brake line got super hot and caught fire which melted the line in half - also melted the clutch cable. any ideas what might be going on. - also seemed the intake got hot as well. newly installed batteries as well as alternator. - Help please. ideas of what might have went wrong?