The original Lucas alternator was sized to supply the car as it left the factory, no more, no less. As soon as you add an accessory, or the alternator starts to get tired, it is no longer able to keep up with the power draw. It is very common to reach home after a long drive in the rain, headlights on, heater on, wipers on, and listening to the game on the radio and find the car won't crank in the morning. the battery ran down while driving. The stock alternator just could not keep up with the load.
To solve this, I sold a 95-Amp GM alternator, with exact foot spacing to bolt directly in place of the stock 35- or 42-Amp Lucas unit. I have these made up specially with a heli-coil in the lower foot to take the existing adjuster bracket and a smaller regulator cover than they normally come with, in keeping with the look of the original.
The only change required is that the Lucas alternator plug must be changed to a GM one. The wiring is simple. In the event that the alternator ever needs to be serviced, it can be done locally at any repair shop for much less than the old Lucas one. The GM unit will make power, even at idle. No more blipping the throttle to turn off the idiot light. Now you can put those seat heaters, big stereos and bright headlamps in and never run out of power.
Update 2/18: If you have a well-stocked auto electric shop nearby I offer instructions on how to have one made up locally. If you have a wrecking yard nearby where you can source a core, the conversion gets even cheaper!
Click Through for Instructions.