I've discovered why my upgrade headlight harness main fuse turned off my headlights unexpectedly on a dark country road and freaked me out! First of all, I hadn't installed a "Putco" harness but a cheap knock-off. It's main fuse was a mini 30amp in an unsealed holder with just a flip cap and had corroded. After cleaning the fuse, it happened again several days later, but this time the fuse holder had melted! I bought a sealed fuseholder with a physically larger size fuse (still 30amp) with 12gauge wires and spliced it in. So far, this seems to be working. It amazes me that resistance heating can melt the fuse holder and not blow the fuse! Also, the harness had what looked like 18gauge wiring, but after removing the insulation, was only 16gauge!

BUY THE PUTCO!!

 

I know what you are saying. I had RR and stator issues on one of my Honda VFR800 Interceptors. I traced down other electrical problems the bike was also having at the same time. There was a fusible type link built into one of its battery cables that was showing as going bad when I tested. I used one of those flip type lid fuse holders to put things back to normal (it was a 30 amp as well).

I was going thru a phase in my life back then. I made a conscious decision to use 2-wheeled vehicles as my only method of transportation for myself. I made it just shy of four years. It was fun.. easily doable living in the south. I rode the VFR thru inclimate weather and many rain storms during that time. I realized the flip type lid fuse holder I used was not an especially well designed unit to use for in this application. It also failed on me too. Moisture and rain ended up seeping into it in relatively short order.

(edited to add):
I was meaning to say the main point.. I got off the VFR motorcycle one day and as I took off my helmet. I saw it smoking. My VFR was on 🔥 at this fuse holder. I saw it was very hot and had smoke rising from the meltdown...

 

This is why since doing my NSS and learning about di-electric grease, I swear by it. It keeps the moisture and therefore corrosion out. I even (where required such as an outside connection) fill my crimp terminals with the grease before putting the wire in and crimping, it ends up sealing the input and the main contact points of the connectors.

As for the resistance heating, imagine 20A @12V = 240W. 20A isn't going to blow the 30A fuse but 240W of electric mostly being converted into heat energy in such a small contact area is why it melts but the fuse is intact.