1994 Lincoln Continental car shuts down

While driving the car may just shut off. Just prior to this the dash panel emits a beep and msg to check engine.
It happened sporatically back in November and not since then, until the car was repaired to replace the gasket on the timing belt cover last week. The next day I drove it and within the first hour it shut off at least 11 times while driven. Later, as I returned home, I drove, first using only the heating. Then added the radio. No problem. Then I add the GPS, which I used earlier in the day and within minutes it shut off. Unplugged the GPS and drove without incident. However, when the problem first occurred I didn't have a GPS. I checked the negative terminal and it seems good and tight, but cannot say the same for the other end. Can you provide any insight and suggestions?