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Just rebuilt most of a 2 stroke jet boat. (if you need / want any boat details, see: this thread)

Yesterday, she fired right up no problem, today she won't even turn over.

After some basic troubleshooting, I determined that I blew the fuse in the CDI box.

Pacific 10AMP

Went to 5 stores trying to find this fuse without any luck, also searched for a similar looking one online for quite some time. The only markings on the fuse is, "Pacific 10A". I bought some generic 10 amp fuses in case I get desperate, but I don't want to put these in and cause more problems. If someone could help me determine what type of fuse this is, I would feel much more comfortable.

Can someone help me locate this fuse, or a comparable one?

I am hoping that the fuse just blew because it was so old, but I know that is pretty unlikely.

I found a loose connection to the boats horn, could this have caused my issue?

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Fuses have 3 different parameters; current rating, voltage rating and physical size.

The physical size is self explanatory, it just has to fit.

The current rating is also rather self explanatory. The fuse protects the circuit against high current. If the current rating is exceeded the fuse blows. A fuse should always be replaced with another fuse with the same rating, never bigger.

The voltage rating is the most confusing one and commonly overlooked. When the fuse blows it has to isolate some voltage. That isolation guarantees that the fuse won't arc over after the fuse is blown. The voltage rating of the fuse just has to exceed the voltage rating system.

As long as all 3 parameters are met, any fuse can be installed.

Loose connections don't blow fuses. Shorted connections do.

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That's what's known as a 'barrel fuse' or 'cartridge fuse' - You should be able to get them at any decent electrical supplier.

The fuse will have blown because it was overloaded - and the most likely cause of this is a short circuit. Before replacing the fuse, try to identify the source of the short. The loose connection you mention is a good place to start, fix that first, and check as many of the other circuits run off the same fuse as you can.

Generally, when you see cartridge fuses in an automotive application, it's an older vehicle, and you often see a lot of stuff running off the same fuse - if this is the case with your boat, it might be worth splitting some of the circuits off to new fuses - this is safer, and makes troubleshooting much easier. You can get aftermarket fuseboxes that take modern blade-type fuses, including waterproof ones for damp environments.

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It's worth noting that there are actually five fuse parameters that are important to consider (and easy to get wrong when buying a replacement fuse):

  1. Current rating (the "size" of the fuse, the amount of current that it is intended to carry).

  2. Fuse characteristics – how fast the fuse will respond to an overload. Fast acting fuses are designed to blow quickly on an overload to protect sensitive equipment, slow acting fuses are used in motor circuits and other applications where the fuse needs to tolerate short overloads without tripping.

  3. Voltage and interrupting capacity – together these determine the ability of the fuse to reliably disconnect a circuit with a fault. The voltage is the maximum voltage the fuse can reliably interrupt and the interrupting capacity is the amount of short circuit current the fuse can reliably interrupt. Higher voltages or currents could result in arcing or other failures to interrupt a short circuit. Some types of fuses are designed so that it is relatively hard to install a fuse of the wrong capacity – but this is not true of barrel fuses, you can get both fast acting and slow acting fuses in the same size.

  4. Size – the physical dimensions of the fuse.

There are lots more parameters, but they are not typically "visible" to the end users. But if you're interested Littlefuse has an informative document they call Fuseology.

One quick check for the appropriateness of the replacement fuse is that the innards should look about the same – if the construction looks significantly different, then you can be pretty sure that the two fuses will have different charcateristics.

Now, on to what could have caused your fuse to fail, it looks like there might be some corrosion on the fuse. Fuses are supposed to trip when the current through the fuse causes the metal of the fuse to melt. But anything that raises the temperature of the fuse will reduce its current carrying capacity. If that is corrosion it could have caused resistance which would have resulted in the fuse heating up and thus tripping.

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