'72 Valiant has no power

Hello everyone, hopefully someone can help me get my trusty '72 Valiant running again.

I went to crank her up a couple nights ago and noticed the dash lights and outside lights seemed brighter than usual. When I put her in reverse the lights got noticeably dimmer. Right then the car just cut off on me. Now the lights won't even work. When I turn the ignition I get absolutely no response. I hadn't drove the car in about a week and it was dark, when I cranked it I thought I saw a spider web near my head but in hindsight I'm wondering if it was smoke I saw in the dark instead.

I cleaned the battery cables and the battery itself tests as good still. The car has the 318 small block if that helps.

I'm wondering if it's the fusable link and if so how do I find out for sure?

Thanks for any help.