Strange problem, never see this before

[obrut]

I have a 86 c10 with a stock 305/th350-c. Tonight I had to run out to the store, I pulled into a parking spot and shut the truck off but it shut off almost like the battery was removed. The head lights, power locks everything had no power with the key in the on or off position.

After about a minute the lights turned on and I could start the truck. I shut it off, ran inside the store came out and went to leave and the same problem. No lights or power to anything not even the brake lights when I pushed the pedal, almost like the battery was remove. Then all of a sudden, its fine, the key buzzer is going off dome light is on and it starts right up.

When I got home and shut the truck off it shut of again like the battery was removed. I flipped the key back to the run position but nothing, no lights, brake lights, dome lights, power locks, radio - nothing. And then all of a sudden without doing anything it just turns on and I have power again.

Bad battery? Something in the alternator? Loose power wire somewhere? Anyone have any ideas or have you seen this before?