Cranking issue

My 85 4x4 22r is having issues. Started suddenly. Brand new battery (checked on tester to make sure it was bad) and 4 yr old alternator ,also tested at parts store. Both battery and alternator are good.
When I go to crank the truck it does nothing. I get no gauge lights,No radio..nothing. when I put jumper cables on it it cranks and runs. Take the cables off and my charge/battery light flashes on the dash.
Do I have a loose ground somewhere? I'm confused...

 

Still having a problem?

Have you removed and thoroughly cleaned the 2 main battery cables?

 

Yes, I cleaned the cables... I removed the alternator and battery and had them tested. They both were fine. The battery isn't but 2 weeks old. The alternator isn't but 4 yrs old.
I put both parts back on the truck and it has been cranking fine ever since..lol Not sure what the issue was. It hasn't messed up again. Guess I will find out next time it leaves my wife stranded in the deer woods..lol