In a nutshell, it doesn't. Not only has amp technology come light-years since 1989, the components used in the JBL amps have degraded over time. Capacitors crucial for proper sound-shaping lose their characteristics, resistors lose their resistance (or gain more), etc etc.
Every Taurus comes with the same connector behind the head unit - an 8 pin flat connector that goes directly to the speakers. This is what you'd use if you were powering the speakers directly with an a/m HU - which, honestly, with 90% of the HUs out there, is going to sound better.
If you're going to use an a/m amp, which I also recommend, you would want to run straight RCA cables back from the a/m HU.
The JBL equipped cars do not utilize the same connectors as a non-JBL car. If your car had the "Premium sound" (one amp in the back), that uses the same connector as the JBL system.