Hey, I pulled my 72 Dart in the drive way & parked under the shed, did not have it backed in all the way, So I went to start it back up & it lost power to everything, No Lights, Nothing, Battery has 12. something volts but the power wire will not arc on the battery!.. So what all can make nothing have power???... I'm thinking starter wire or fusible link!

First two things I'd check would be dirty battery terminals or blown fusible link.

Check connections through your bulkhead...

Do a load test on the battery as well.

Use a volt-meter (or a test light as a last resort). Check voltage between the battery posts. Move to the battery cable ends at the battery and check voltage. Same is good, drop indicates a problem. Move the negative lead to the block end of the ground cable and test. If good, move the negative lead back to the battery and start down the positive path. Other end of the positive cable, starter relay, firewall positive connections, etc. Jumping around checking random places is a waste of time, and you should be able to locate the problem in less than 5 minutes if you follow the path of the power and see where it stops.

After following 'nuthinbutmopar's advise, and if it's past the Fusible Link, I'd check for continuity across the AMP Charge/Discharge gauge on the dash..

I just dealt with this exact same thing on my 69, 340 swinger. I daily drive it in nice weather, just came back from a drive to the lake on a weekend, 2hr round trip. Shut it off, went in the house for 10mins and came back out to put it in the shop. No power, I spent a weekend chasing down and checking everything pertaining to what would need checked. In my story, the batt was junk somehow of all things. Check the simple stuff and go from there imop.

all good advice here.
the worst will be a bad battery.
other than that, it will end up being something simple.
bad thing about that is, you have to find it !

Battery to battery post on starter relay. Fuse link on the same post to firewall bulkhead. Inside firewall bulkhead to ammeter. Ammeter to a multi wire junction in the harness.

Fuse link or ammeter. Also, confirm the bulkhead connection is not burnt up on both sides of the firewall.

Ammeters fail. Old bulkhead connectors get hot and melt. Fusible link would need a short somewhere to make it burn.

Check the battery wire on the back of the alternator. It is on the harness side of the ammeter.

Down and dirty fix for the ammeter is take one of the wires off and move it to the other stud so they are connected and not running the current through the meter.

It was something simple, lol I panicked & did not think, got to look at it some more after work today!.. I have the temporary battery terminals on my Dart & the 2 top bolts worked loose on the ground!

GOOD ADVICE!!!!
I recently chased my tail for about 5 hours as my V checks kept showing 12V but every time I tried to start it NADA, yet it had started perfectly 10 minutes earlier.
I did not even consider the battery as I have NEVER had one fail like this in over 50 years, so i proceeded to chase my tail. It was only by chance that I had the meter hooked up and watched it drop to 2v with a load and quickly recover to 12. It was showing V with no load, but had no Amperage/ Current

I have since read this is becoming a not so uncommon occurrence as the battery MFR's are cutting costs by using thinner plates and connections inside the batteries
I will say it was on a tractor with a bunch of safety interlocks so I ASSumed that one of them were at fault again. I can tell you I will not get stung on that one again

yes this ^
my first check would be to trace battery voltage from the small wire on the batt terminal up through the bulkhead. that is how voltage gets to the ign switch to power everything up.

glad it was something simple, and you found it.
however, that type of cable end is one of my most hated electrical items ! whenever i see those on an otherwise nicely detailed engine bay, i cringe !
you have correctly identified that as a TEMPORARY terminal end. please install a new, permanent end if the cable is long enough to do so, or replace the cable[s].
it will be better for you in the long run, and i won't get the jitters just thinking about those ends.

those things are absolute CR-P