'68 etype voltage issues

[Sebring]

Hi All, I have an issue that his stumping me.

I installed a vintage air system in my car. However, when I turn the fan on, the voltage meter drops from a healthy 13.5- 14 to about 12. As such, if i run the car for an extended period with the fan on, my battery dies.

The alternator appears to be a stock unit as it continues to employ a voltage regulator. The back of the Alternator sates "Lucas" with no model number.

Likewise, even without the fan on, the dash and headlights get brighter as I rev the car indicating a non-constant voltage.

The car is new to me and I don't have any history on it.

Thanks
Paul

[cactusman]

Not sure what a vintage air system is but it rather sounds as though the alternator is not generating much output. The voltage at the battery should be around 13.8-14.2 at anything above 1000 rpm with an alternator and unless your air system uses 40 + amps the alternator should be able to supply all the power it needs when the engine is running.

I think you will have an old style Lucas alternator with a separate 4AW (I think) regulator (small black box with three wires under the heater box) so it may be the regulator that is dead. Try replacing that first.