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Member
Joined: Aug 19 2019
Posts: 38

I think I need to replace the alternator (maybe voltage regulator). Lights steady before starting the engine, as soon as it's running, lights go noticably brighter and pulsate, seemingly faster with higher RPM. My voltmeter across the battery reads steady at 14.5V at idle and steady 14.4 with some RPM, but the pulsating is probably too fast for my meter to notice (several times a second).
It may have been doing this for months and I'm only noticing now with the winter darkness. With all the electronics I probably shouldn't let it go very long?

Member
Joined: Dec 29 2015
Posts: 712

Miah's was doing that, not sure if it ever entirely stopped. It seems a fair enough bet that it's the diode pack in the alternator.

Member
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Joined: Dec 30 2015
Posts: 3832

One of the diodes has gone open circuit in the alternator. Alternator generates 3 phase AC which is then rectified by the diode pack. With one down only two phases are being rectified so it shows as the pulsating lights. Better that way than when one goes short circuit as that can flatten your battery in about an hour whenever the car is left.

Member
Joined: Aug 19 2019
Posts: 38

Thanks for the replies. I'll try a spare alternator tomorrow.

Member
Joined: Aug 19 2019
Posts: 38

Spare alternator fixed the problem.

Member
Joined: Dec 30 2015
Posts: 1650

Good to know. Thanks for posting the result.

Member
Joined: Aug 05 2019
Posts: 9

Interesting. Mine had the pulsing lights issue a while ago, for a few months. Now the issue has disappeared. Nothing has been touched. Running voltage is stable at 13.7V. I’ll need to find a digital oscilloscope and look at the output wave form and see if it has an AC fluctuation.