87 t-bird faulty charging system or electrical problem?

First check the voltage at the Alternator output terminal with the engine running, should be ~13.5 volts or better.If not, suspect the voltage regulator. Folks tend to forget about it. It can be tested, but it's 17 years old and cheap. For ~$15, replace it and have peace of mind.(Of course check all of the connections first). Then check the voltage at the battery terminals, engine running, should be ~13.5 volts or better. If you get less than 13.5 Volts at the terminals, suspect the line between the Alt and battery. If both are low, the "new" battery could be shorted internally, or the alternator could be defective. Many testers do a voltage test. This can be misleading if the voltage is ok under test but the Alt can't produce under load. The main suspect is the regulator. Tom

"wilnbon" wrote

Digital speedo with fuel gauge, temp gauge, and alternator "idiot" light? Does the alternator light come on with the key at "on"?

The alternator gets its "start-up" power through that light, or a built-in resistor if the light happens to burn out. Once running, the alternator is self-energizing.

If the light doesn't come on, the bulb may be burned out, one of the wiring connectors on the back of the gauge cluster may not be plugged in all the way, there could be a broken wire somewhere under the dash (anyone been messing around under there, like cutting wires for a stereo?), or the ignition switch may be faulty. Do the back-up lights work? They get power from the same terminal on the ignition switch as the alternator light (and several other things).

does your have external regulator ?