Fusible Link *Fire*, battery not holding its charge

[DoubleYOOHZ]

Hello Z Community, 

I am coming back in hopes to revive my Datsun once again. Before I jump back in I want to give a back story to this situation. 
Car has been sitting in garage for the past 9 months. I charged the battery in hopes to get it cranking and starting again. After some attempts of failure, I left the car in the ignition and turned to "on" (where you hear the buzzing). Fire ensued. The fusible link for the Alternator/Ignition Relay link caught fire. (diagram below)
 

I replaced the fusible links and charged the battery.  It can be seen below (black). (You can see some of the fire aftermath at the bottom of the fusible link. It is like a pimple)


Car started to idle rough but then idled perfectly. However, it can not hold its charge. I would attempt to drive the car the next day, but it would struggle to crank. So i made sure I charged the battery again and drove the car around. Battery is new. From previous attempts(previous thread), we did test the alternator and did get a charge. I wanted to ask the community, what is withholding my car from holding its charge?

I do want to mention, there is an aftermarket radio that was installed in the vehicle by the previous owner. A friend suggested that improper installation caused a short circuit and was the leading cause of the fire. I pulled the radio today and found copper(or some metal exposed). Would this have instigated any issues to what has happened to me? (pic Below)
 

[SteveJ]

Year?

[DoubleYOOHZ]

15 minutes ago, SteveJ said:

Year?

1977 280z. Sorry, i left that out. 

[SteveJ]

Did you check your voltage regulator?

[DoubleYOOHZ]

13 hours ago, SteveJ said:

Did you check your voltage regulator?

In the process of replacing it now. I will update once it is done.