It’s a bad idea in general to purchase a control panel without reading all of its associated documentation because without a thorough understanding of the control panel, you cannot be sure that what you’re buying
- Works
- Is actually an FACP (and not a releasing panel or dialer or NAC booster)
- Is likely to be useful to you.
If you cannot understand at least the diagrams of the manual, then you should not purchase the panel.
One of the big indicators to me that you have not done your research properly is that you do not know what/where the CPU is. In your video you were indicating the on-board annunciator assembly as being “peeled up.” However, unless the connector that links this on-board interface with the control board has been damaged, it’s likely the interface itself works fine. That being said, I would not continue bending it, as flexing the board can and will cause damage. Also, the missing pin holding the panel door is of little concern. That can be repaired later on
Now since you have already got the panel, here are my recommendations:
First off, DO NOT give this panel power before you can verify where the AC connections are. Aside from being incredibly dangerous to you, if you apply AC improperly, or to the wrong terminals, or without the proper grounding, you WILL kill the panel.
Second off, DO NOT apply battery power to this panel either. Starting the panel on batteries can and will destroy the charging circuit. Most modern panels won’t do anything with the batteries unless there’s AC, but you can never be sure.
Third off, BEFORE you even open the panel again, OR even CONSIDER applying power, I HIGHLY encourage you to find the manual online, and read it cover to cover.
I encourage you to read this post:
<URL url="So you want to buy a FACP...]So you want to buy a FACP...]
And gain some insight into some of the principles of control panels.
Finally, here’s a manual for your panel:
http://firealarmresources.com/wp-content/uploads/2013/06/Simplex-4004+Installation++Operating+Manual+Rev+C.pdf
I recommend you read it cover to cover, and pay close attention to the circuit diagram in section 1-3. Let us know what you think it’s telling you, and we will be happy to help you try to get this panel operational 
*my only edit was to fix a typo at the top