My 93 explorer holds a charge when the vehicle is running but once its started it runs off the battery instead of the alternator I have replaced both the alternator and battery and I still have the same problem

. Check all under hood and under dash fuses with a test light or multimeter:

https://www.askmehelpdesk.com/cars-t...tml#post252145

. Check the regulated battery voltage, as described in the link below:

https://www.askmehelpdesk.com/cars-t...ml#post1973613

Some rebuilt aftermarket alternators are pathetic. It's not uncommon to have to exchange one for another. Also, be sure to clean the mega fuse wire, which goes from the alternator to the under hood fuse box. They can become terribly corroded and greatly reduce the charge to the battery. Clean it with abrasive cloth and coat with dielectric grease, in order to be military ready. If the problem persists, have the PCM tested. Here's where I'm going with this:

Check Alternator FR (Field Response) Signal. Have alternator inspected, if idle speed fluctuates with electrical load. The FR signal communicates to the PCM how "hard" the alternator is working to meet the electrical demands of the car, including the battery and any loads which aren't monitored by the ELD (Electrical Load). This square-wave signal varies in pulse width, according to the load on the alternator. The PCM places, approximately, 5 reference volts on the wire. The voltage regulator will drop this signal to approximately 1.2 volts, in proportion to alternator load. The PCM compares the electrical load (ELD) signal with the FR (Charging Rate) signal from the alternator and uses that information to set the idle speed and turn the alternator on and off. This helps fuel economy.

. Disconnect the negative battery cable and then clean the connections going to the mega fuse, located on the end of the under hood fuse box. Afterwards, coat connections with dielectric grease.

The odds are that the problem resides with the alternator or with corrosion.

May God bless and protect you.

I have a 93 ford explorer and I have replaced the alternator twice now going off what Texas grease monkey told me and it still runs off the battery when its running the voltage regulater comes with the alternator and the power is getting to the alternator but not from the alternator back to the battery?? I've looked evrywhere and I still can't find the problem and suggestion would help!!

. Disconnect the negative battery cable. Remove the connector from the alternator and, using a multimeter set to ohms, check the continuity of the connector and wire going to the battery (mega fuse). There may be a problem with the connector or the harness (internal break). You can buy new ones (alternator pigtails and charging wires) at most auto parts stores.

. Check the mega fuse (likely 130 amp.)