I have a 2000 Ford Taurus flex fuel vehicle ,installed new alternator and it still won't charge also instrument cluster not working,have checked ground strap to motor,three ground wires to ECM plug

charge the battery fully and have it load tested. if all fine hook up a multimeter set on volts dc to the battery while the engine is running. you should have 14+ volts if not then your new alternator is bad. happens a lot with aftermarket alternators. if you have to replace it, go OEM.

2nd alternator had both tested and they show good,not getting 14+,only have battery voltage,getting signals to voltage regulator,according to schematic it goes back through voltage light in display,tried different display,no difference

Also grounds for both trace back to ECM

If you are only getting battery voltage, then they aren't good. There is one thing to check though and you might have to call a ford dealer service depth for confirmation. On some vehicles voltage regulation takes place in the pcm, not the alternator although I think that might be more common on dodges.