Really, really, unlikely that the fuse would blow due to a defective relay. The relay only is a fused connection on the circuit in question. Blaming the relay would be similar to blaming the fuse box for the reason the a fuse would blow. Not unheard of, but almost.

The fuse blows because the circuit uses more current than the fuse is rated for. This means that the device that the fuse powers is using too much current or the circuit is shorted somehow.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician