93 240

When driving about 20 minutes the instrument panel lights blink all at once, except for the ABS light which cuts on too but not as often as all the others. They stay on until I accelerate. I cleaned the battery contacts, because two weeks I went to wal-mart and they checked the battery while changing the oil, but no real problems, just in case they did something wrong. I got the same symptoms when the battery hadn't made good contact on the negative pole. I clean and tightened it and it worked okay. I went to the store feeling victorious and then it happened again. This baffles me. I don't know what this could be, the battery contacts are there, the car starts fine. I am afraid to drive the car long distances. This just started yesterday while idling in traffic. Any ideas?