1992 Ford Crown Victoria Help! New battery & alternator

Electrical problem
1992 Ford Crown Victoria V8

First incident, car died at a stoplight during daylight hours. Lights and accessories worked but were dim, the volt meter on dash was at lowest point, and starter would only click. Car started with a jump, but wouldn't stay running, so figuring maybe bad alternator, jumped it to start again and disconnected negative battery terminal which made it die. Then put in different alternator from another '92 CV, new battery, and replaced terminal ends (which had been badly corroded). Car ran fine for about a week, until second incident, again during daylight hours the volt meter started dropping and the car slowly powered-down and quit again. Same dim lights and clicking. Traded battery which tested "replace battery" at Wal-Mart and old alternator tested 2 out of 3 at AutoZone. Now have put in a brand new alternator and battery, but volt meter reading still pretty low. Even did the negative disconnect and it died with new alt! Is this a wiring problem or what?