What is completely draining my truck's battery?

We have a 1980 Ford F100 Flareside. We just bought a brand new battery and the alternator is fairly new. We have been working on it so we haven't started it in about a week. No lights left on, no anything left on.

Today we hooked up the wires to the spark plugs in the correct firing order for a 351. We then tried to start it up. Husband put the key in and the headlights turned on and immediately dimmed out completely. While trying to crank it, it didn't even click or attempt to turn over.

We tried to jump start it. Nothing! Not even enough to turn the lights on at all. Made one click noise.

What besides an alternator could we check. I've heard of parasitic drain, of course we can't find our meter in order to do that. But, battery is completely gone. Brand new

Since you have an old Ford the Fusible Links are attached to the Starter Solenoid on the inner fender. After you charge your battery hook it up and look when you attach the ground to see if it arcs. If it does remove the ground wire. Take the small wires off the big stud with the battery/starter cable. Tap the negative terminal to the battery post to see if it still arcs. If so, unplug the alternator and check. If not replace the wires one at a time and check. When/if you find the offending link look at a schematic to see what's on that circuit. There will be plug in fuses… Pull them one by one and check. If you don't want to do that look on Craigslist for Mobile Mechanic. PS You can't jump thru a dead battery. Best to charge is low and slow 2 amp trickle overnight is what I do.