92 Bonn electrical problem

Hoped in car it turned over strong, drove it about a block,shut it off. When I tried to re start 5 minutes later it acts like it only has a few volts in battery. Horn barely blows and headlights weak. Then suddenly lights are bright horn blows strong but when I try to crank everything goes weak again. Cleaned connections at battery (no help), turn lights back on, weak still, then boom lights go bright and strong again but when I try to start, weak again. Will test with meter tomorrow and will also check connections opposite battery. Any ideas? I know the battery is ok.

Maybe Battery Cables Are Bad Rotten Under Outer Wire Case

Was a bad battery.