Pulsing headlights

Your alternator (rectifier, regulator or brushes) could be on the way out. Does the alternator charging light come on (could be very dim) when you have the lights pulsing?

 

Robert, it does indeed sound like an alternator issue. One means of checking that would be to monitor the voltage at one of the main distribution points (battery, battery connector in engine bay, main feed to footwell fuse box) as you drive.

It could be something as simple as a loose belt. IIRC, there's a cooling duct for the alternator that picks up air from under the car. If it was splashing a bit of water on a belt that isn't tight enough that could cause enough slippage under load to lower the alternator output enough to notice.

The fact that the alt was recently worked on might well actually be a clue. The old adage is to check the last things you touched first.

Good luck & let us know what you find.

 

Wouldn’t we expect the lights to dim, rather than get brighter? I had a slipped belt once and had no signs except a v faint glow to the warning light.

That said, could it be that the bright is normal - under revs for example - and the normal is dim due to an alt fault or possibly a loose earth that is occasionally making better contact?

If it had been a more regular switch between dim and bright, then given the rain and night I’d have suggested it was the wipers only clearing in one direction!!!!


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Agree that the lights would dim when the belt was slipping, but when you're driving it's not easy to determine whether they lights are really getting brighter or if they're just returning to normal brightness. Belt tension is pretty easy to check compared to a lot of stuff. If you're as lazy as me you'd rather use a voltmeter though.

It'd be interesting to know if the same thing keeps happening in dry weather. If it's rain related that points more to the belt than anything else, but it certainly could be the alternator itself.

 

voltage regulator is wacked if light get brighter

 

Do you think it could be the cooling fans cycling? That usually causes a high current draw and the lights will usually dim. AC Clutch cycling will cause similar results.

 

Hopefully It was just a bad part on that rebuild.

It happens.