The security system has nothing to do with cranking. For a much better suspect, based on your description of, I'm assuming, the dash warning lights, follow the smaller battery positive wire to the under-hood fuse box. Clean or tighten that connection. While you're at it, also follow the smaller negative battery wire to the body sheet metal. Be sure that connection is tight and not rusty.
If that doesn't solve the problem, we'll need to dig further. You'll need either a digital voltmeter or a test light. If you aren't familiar with using them, check out these articles first:
https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester
https://www.2carpros.com/articles/how-to-use-a-voltmeter
They're using a voltmeter with an "auto-ranging" feature. That's an expensive feature you don't need. You can find both of these tools at Harbor Freight Tools for $7.00 or less, and at Walmart or any hardware store. I can help you set up the meter if necessary.
Let me know what you find.
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Saturday, August 19th, 2023 AT 8:19 PM