Larry,
Fuses are installed in circuits to prevent fires and to protect the wire, not the equipment. It is expected that the equipment will have its own protection.
Each gauge of wire is rated to carry a certain current and should be fused no higher than that current limit. For example, most 12 gauge multi-strand wire is rated for 20-25 amps (depending upon the specific installation) and should not have a fuse above that rating. If you install a 40 amp fuse ahead of a 12 gauge wire and that wire shorts to ground with a 39 amp current, the wire will melt (and possibly catch fire) and the fuse will never blow. Your 30 amp fuse was too large for the wire.
The fuse holder is also rated at some maximum current, although I don't know what that is. I would think that 30 amps would not overload it, but I suppose that it's possible that your fuse holder was itself overloaded. The limit current should be stated in the documentation that comes with the fuse holder. I don't know why yours burned up. I would replace it with a fuse holder rated at 30 amps or above.
Then replace both of those 30 amp fuses with 20 amp ones. The first fuse in this circuit (for the main power to the pusher pump) should be as close to the battery as you can get it. This is the only fuse you need in this circuit.
The control circuit side of the relay is the wire that powers the engine-mounted factory fuel pump, correct? This wire is already fused via the truck's wiring. It does not need an additional fuse.
What's the 10 amp fuse for? If you fuse the circuit at the battery and keep 12 gauge wire all the way to the pump, you should not need an addtional fuse.
My pusher pump draws less than 15 amps. (I don't remember the exact measurment - It could be a lot less. ) A 20 amp circuit should provide ample power.
If the pump runs when it's powered directly from the battery, then it's okay. No, the 10 amp fuse will not necessarily blow if the pump goes bad. It depends on the manner of failure of the pump. If a wire shorts to ground, the fuse should blow. If a wire just breaks, creating an open circuit (like shutting off a switch), then the fuse will not blow.
Except for the extra fuse, which should do no harm, it seems that you wired this correctly. If your circuit won't work with a new fuse holder, then check the wires themselves. It's possible that one (or more) wire has melted due to the oversized fuse. If so, you're lucky you didn't have more serious problems than a pump that won't run.
Good luck,
Loren
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