My daughter has an old 1.3 litre engine Ford Laser. The idle speed is normal
until the headlights are turned on. Then it drops by about 20%. When the
brake lights come on there is a further drop in idle speed, until the engine
occasionally stalls. Having dabbled in car engine repair and car electronic
repair I have never come across this. Can this be an alternator problem
where it puts too much load on the engine under heavy current? If so, what
would it be about the alternator that would cause this? Can it be a
non-electrical problem?

Thanks for any advice.

Henry.