Add me to the "hidden fuse" club

Yep, that looks familiar, had the same thing with my car. There are several threads that suggest the replacement be a 30 amp gold cartridge type that is commonly used for stereo systems. Same rating but much more robust. You just have to cut the wires leading to the current fuse set up and replace with the new one. I'm bad, this is one item I have been putting off doing and just have to get around to it.

 

So much overkill on mine that it works with just a 20 A fuse. Plus it's accessible directly under the small cover.
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I spliced in 10 AWG stranded but the really fat stuff came with the fuse holder (Autozone). Not sure what size that is.

 

Just replaced my "hidden fuse" with a 30 amp aircraft circuit breaker. I would investigate why the fuse melted. Remember there are several motors and components in the HVAC system that can bind up from lack of use and cause a high current draw causing this very problem. Don't wait till the wiring catches on fire !

 

My ignition cut out last Friday on the way to storage. I had just washed it and did soak the engine cover. I had the ac on as it got warmer out and did a down hill right hand turn. I pulled over o a back road and started it back up again. No problem but I did turn the ac off. I have a feeling something might short like wires to and from the compressor or such. AC did work again but I have NOT removed the carpet to look at the fuse.

 

+1

I've seen several photos of burned 348s where the fire appeared to originate from the bulkhead area (under dash or HVAC). Replacing the fuse and holder doesn't fix the cause of the problem. Not the final fix anyway.

 

Jeez...you soaked the engine cover?

Why...?

You just soaked your engine, transmission and complete rear suspension.

Not good

 

The main reason why the AC fuse melts is corrosion of its pins and the sockets which crates resistance (loss of good contact) at the connection points. This causes micro-sparking at the connections, overheats them and melts the fuse. It is not due to over-current due to a faulty component, other wise the fuse would just blow, not melt.

Another point to check (clean from time to time) are to connections to the AC relay, especially the connection of the thick brown wire (see Wade's picture below). I believe that the reason for corrosion of these parts is the moisture accumulation in the boot (and age).

 

Sorry, forgot to attach. Note the overheating of the brown wire connection also at the relay.
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Yeah, it was pretty ugly. One of the connectors nearby as well (which I cut out entirely, splicing the wire together).

Replaced the burned relay:
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Before replacing the relay and fixing the brown wire's connector (and after replacing the melted fuse) I used a laser thermometer on these hot components, up to 200 degrees as I recall. Afterwards, all is much cooler now.

 

Excellent point. There is a copy somewhere in FChat of a TSB from Ferrari back in the 90's suggesting the replacement of the fuse with the cartridge type to eliminate the above so they were well aware of the problem.