When I replaced all my fusible links with fuses, I also put an 80 amp fuse on the thick wire that comes from the alternator to the battery. This worked fine for about a year and a half but a few days ago the fuse died. I put a new one in and within a mile of driving the fuse and holder were a smoking pile of melted plastic. I just replaced the voltage regulator today and after about a minute the wire was getting hot so I pulled the fuse and drove home. What could be making that wire get so hot?

 

Well it sounds like your fuse is too high amperage rating. Instead of blowing from over-amperage it's cooking the wiring.

I'd take a close look at all the grounds, including voltage regulator grounding.

 

Your Nippon-Denso alternator is rated at 120-amps, if you use an 80-amp fuse on the charge wire it will eventually fail from overload, after starting your engine the alternator is going to try and produce maximum current for a short time to recharge the battery especially in the winter when your grid heaters are activated, they are rated at 200-amps each.

Use at least a 120-amp maxi-fuse and upgrade both the alternator to battery wire and the case ground to battery wire using #2-gauge welding cable.

The wire could be getting hot and melting because of a loose connection at the burned wire, when a fuse holder overheats, the spring clip looses tension now creating loose connection on the new fuse.

Also check your battery voltage, you could have 1 shorted cell creating a 10-volt battery and your alternator will try to push 120-amps @13.8 volts into it and since the fuse is the weakest link it will melt.

I have a 200-amp "T" fuse on my alternator, it is only for a catastrophic failure of the wiring or the diodes on my 160-amp alternator.

Can you connect a DVM and tell us what the battery voltage is (engine off) and the charging voltage is at a fast idle?
Jim

 

My info regarding fuse amperage rating was incorrect, thanks Jim Lane!

 

I should mention that I had to get a new fuse holder since the old one melted so bad. I watched the volt meter on the dash when I ran it yesterday and it only got up to about the first mark. I will check the battery voltage today after work.

 

Ok update on this: I have now replaced the battery, alternator, and voltage regulator. I put a 175 amp fuse inline and it popped that as soon as I got on the road (RPMS going up) from the parking lot where I put it in.

Just now I replaced the wire from alt to battery and the green one from the alternator to the voltage regulator. Now when I started it(had to jump it) it doesn't charge at all, where before it would charge at idle but once I get off my driveway onto the road (again, getting RPMS up) the fuse would blow almost immediately.