My 1969 Mini is running an old Lucas alternator. When engine is idling and I turn on the headlights the revs drop, then I turn on the high beam and the revs drop more. Is there a problem and if so please how is it fixed?

Theoretically, this is quite logical. At idle the engine is producing juuust enough power to match the load imposed by engine friction. If the battery is depleted (by cranking the motor to start) then a bit more load is introduced and something has to compensate... more advance or perhaps some extra fuel???

More load (ie lights - my high beams consume about 1/3 hp - by my mental arithmetic - happy to be corrected). More load = more vacuum = more fuel (unless you have vac advance which may partly compensate???

If the mixture can't compensate then revs must fall (less revs = less friction = less load)???

Laws of physics prevail....

If you have bad wiring/ connections then heat (more load) is being generated......

Have you tried blipping the throttle ...do the lights get brighter???

Cheers, Ian

That sounds like a normal functioning alternator to me.

The higher the demand on the alternator, the higher the effort will be to spin it. I like to have my idle a little high, so the times when you’re driving at night with the wipers on it still has a decent idle

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I guess I am used to modern cars which are more better at these things.

Modern cars have ignition control, electronic throttles or idle air control valves that regulate the idle speed.

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Simplest is to turn the idle speed up a bit

You could install a new alternator, they are more efficient

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