A seized auxilliary water pump will take out the amplifier. Check your pump. You should fuse the auxilliary water pump with a low amperage fuse so that if it seizes and starts drawing excessive current, the fuse will blow before the amplifier burns up.
Search on auxilliary water pump fuse kit. There's a member here that has a nice little inexpensive fuse kit to solve the problem.

Here it is:
http://www.peachparts.com/shopforum/showthread.php?t=242553&highlight=water+pump+fuse

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