The car is a 88 TBI 5.0. It happened yesterday, as I was driving the motor would shut off, radio died, and everything in the dash died. I pulled over and tried to start the car and nothing happened. The battery gauge read 9 volts. You could very slightly here the chime working. When I opened the door the interior lights were bright. After a few minutes the car started right up like nothing happened. It did it about every 20 minutes afterwords. What should
I check?

 

Alternator and battery