OK, first, the thing under the driver-side battery sounds like the ABS module, the ICP is in the front of the drivers-side head.
But, what you're describing, all these clicking relays and modules, sounds like low voltage or low current capability to them. Connect a volt meter to the Outlet (cig ltr) in the cab and see what's there before and during the crank attempt.
How are your batteries? To test them you need to fully charge them on a charger and have them, individually, Load Tested at a high rate (not the 100A the Auto Parts stores have, you need more like a 300A draw)
Next would be cables... How do they look? Any Green or White powder? You need to check them All, Both sides, to know if the amperage the batteries can supply (if they're good) can get to everything it needs to. Take them apart, scrape/clean/grease/tighten to make them right.
That's where I would start