Hi Cecil,
As per the Lucas documentation, first establish that the generator can produce adequate voltage. Disconnect the D and F wires from the generator and connect the two terminals. May be easier to disconect the D and F wires at control unit and clip them together. Then measure the voltage between the connected wires or a generator terminal and ground. This should rise with engine speed to above the required 14-15v or so. Do not over rev!
Provided the generator is working, next I would play with the voltage regulator setting to see if it impacts the voltage going to the battery. If you cannot raise the voltage, then something else appears to be the issue - bad wiring, bad battery, etc.
Regards,
Clive.