If you turn the key to start and get a series of clicks that's usually an indicator of a weak battery.
If you turn the key and get a single click that is often something to do with the starter. But the starter click I wouldn't call "faint". It was pretty audible

 

When turning the key away from LOCK, the battery dies to 6V after fully AGM charging. Does that mean my battery is done for? Also, are there some things in the system I should look at that may have caused my battery to decay aside from possibly being old? This will be the second BlueTop Optima battery it has killed.

 

I had an optima yellow top in my 85 for years and it never died on me, probably an exposed wire somewhere that's grounding out on the frame or body.

 

I think I got it figured out!First I had the battery load tested and it was still good! I went to check my alternator cables first and those checked out good. I then went to the starter. I had retained the old starter cable and the new 0/1 OFC I added. I took away that old lead and the truck fired up every time.

It must've been looping enough to kill the battery trying to start. My radio doesn't work now, however, I'll look into that next. I'm going to test my luck in the morning, fingers crossed that was the issue.

 

Could you send me the diagrams if you still have them? I appreciate it, iseethings49@gmail.com. thank you