If it cuts out, check what appliances are still available.

i.e. interior lights?
Check for all appliances which work without key, such as central lock/unlock, reading light, glove box light and such.
Can give you an indication if "all" electrical is concerned or just those under the ignition key.

Also look at instruments, still some readings?

 

when it cuts out i have nothing at all no instrument panel no dome light no headlights no radio no pwr windows it kills everything just got a different fuse box gonna swap and see if that does anything but if there short in harness not gonna help at all

 

was thinking bout swapping the ecm out but idk can just change them out or if have to have it programmed seen people say u can just do it with your key

 

i have noticed that my fuel gauge isnt working anymore dont know if that has anything to do with it cutting out

 

Your problem is much more basic. The ECM does not control all power. For the time being I would not mess with that.

If you loose "all" power, even that to appliances which are wired on buses which are "HOT AT ALL TIMES" it could be closer to the battery and the main fuses.

Another question as this has been an ongoing source of problems:

Has the electrical system been modified? (Has there been an addition of i.e. a winch, light bar, stuff like that? Massive audio system?)
Has it been tampered with? (Such as flying wires to power stuff because of a previous owners problem solving?)

Do you have some rat's nests of wires where somebody tried to fix stuff? Wires with tape insulation etc.?

And finally how do the battery mains look? Are the terminals sound? Are the main cables sound?

 

Well yesterday swapped out fuse box see if that help and did notice half the wires under fuse box were cut and taped back together idk why can upload pic tonight when off work wondering if should take them apart and redo them see if they corroded

 

Battery terminals and cables look good as far as i can tell

 

I would re do the wires, if they have been cut and taped, probably a quick job and some either came loose, or have some corrosion in them now. It will atleast give you piece of mind if they arent bad, and covered properly.

wondering if there was a problem with such wires before.

 

Yeah wondering the same thing gonna take tape off them and check them all out and redo them like u said piece of mind

 

IF the battery suddenly disconnects, there should still be power from the alternator, although itll be around 8V DC and extremely noisy. The battery isnt there to "filter" the ripple from the 3 phase alternator.

Put a voltmeter on the battery and read it when it fails.

Look for a flaky fuse link.

Its also possible for battery acid to seep into the cable and travel a LOOOONG way between the insulation and wire. Might be a corroded and broken wire.

I saw battery acid residue on my K5 starter....