Fuses keep blowing at the battery

[Pontooncrest11]

the incident fuse keeps blowing when I try to install new one, its a 20 amp on the pontoon boat

 

[Scott Danforth]

welcome aboard

you have a short somewhere

grab a DVM and start troubleshooting.

 

[Silvertip]

If it is blowing a 20A fuse it's a "big" short (meaning it should not be difficult to locate). Check the positive wire (the one with the fuse in it) as they tend to run over and through the framework of the boat. Disconnect that wire wherever you can get at it at the helm. Then try a new fuse. If the fuse still blows, you found the problem. If the fuse holds, the short is at or after the helm. Disconnect one item at a time and try a new fuse. If it still blows, reconnect and disconnect another load. Repeat, repeat, repeat. If it appears you need lots of fuses -- that would be correct. Or you could disconnect all loads, insert a new fuse and reconnect one at a time until the fuse blows. That device/circuit woud be the problem.

 

[Texasmark]

What does the fuse look like where it separated? If it looks like it melted and fell out of position you have something consuming excessive current, a hard to trace problem. Start by looking for corrosion on the fuse/fuse terminals themselves. If the fuse stays intact long enough, the problem will be hot to the touch when it shouldn't be. If the fuse has exploded, splattering particles all over the case of the fuse, you have a dead short and that should be easy to find:

Disconnect the battery + and as Scott said, get a Digital Volt/Resistance/Ammeter, on the lowest Ohms scale and get on the down circuit side of the fuse with one lead and the negative battery cable/terminal with the other. The circuit resistance for a 12v 20 amp circuit at full current would be 0.6 ohms. That is about what your meter leads read when you touch them together for zeroing purposes. So you will be looking for a reading of between 1.2 and 0.6 ohms. Start disconnecting things till you get a high reading and examine your "smoking gun".

While your battery cables are off, clean up the terminals before you reinstall them.