E34 Electrical Issues - Fusible link?

Hello! I am new to the E34 community, as I'm buying a very clean, E34 - with one exception: It doesn't start and has been sitting for 18 months. Today I went over and tried to jumpstart it.

We got dash lights and dings, which it hadn't had before, and we were able to get a repeating clicking noise (i forgot what it's called), but the engine wouldn't start. I checked the fusible link in the front, and found a small crack. I already have a replacement on order, but I was wondering: would I even get any dash lights at all if it was really the main issue? What could be some other things causing these issues?

Also, how do you access the battery under the back seat? I pulled and pulled on the backseat but it didn't budge, and I really don't want to break it.

Tomorrow night I am going back over to replace the fusible link and put some new gas in and try to start it again. If I could get any advice on other things to try incase that doesn't work, I'd appreciate that very much. Thank you!