Diagnosing pulsing lights

[Whaanga]

I’m working to learn the cause of why my headlights and interior lights pulse at low RPM’s. The pulsing directly correlates with the speed of the engine. I’m getting full battery charge from the alternator so wonder if the issue resides with the voltage regulator? How do I test the condition of the voltage regulator?

Or if it turns out that mine is in good shape, what else might cause the pulsing lights at low RPM’s?

Thanks
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Late 1973 Bay w/a transplanted 914 Engine

[telford dorr]

A bad alternator diode can cause this, as can a slipping belt, loose alternator wiring harness connection, or funky mechanical voltage regulator (the electronic ones don't do this).

For info on testing the regulator, search the Gallery for Alternator Voltage Regulator Test Setup, and read the entry notes.
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'71 panel, now with FI
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Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[mikedjames]

Old electromechanical regulators have electromagnets and bimetallic heater elements and contacts, and they bang-bang modulate the field connection by opening and closing the contacts, turning the field on and off, with the heater controlling how long the contacts remain open for.

So the battery voltage goes up and down, lights dim and brighten, but the average voltage is correct.

If you have any cheap LED lights with resistors and three white LEDS in series , they will dim and brighten even more noticeably.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[timvw7476]

yeah, non-electronic regulator will do it, along with a tired battery, battery connections needing a good cleaning, seems when the battery is about done the connections need more & more attention. Also running a modern stereo with the memory wire (yellow) always drawing the battery down doesn't help matters.

[Whaanga]

Thanks for the replies.

The battery is about four years old. I keep it in the house in the winter.
I don’t even have a radio. And I have no LED lights any where.

Can I pull the voltage regulator and rest it per Telford dorr?
Should I start there?

I’m much more comfortable with mechanical work than electrical.
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Late 1973 Bay w/a transplanted 914 Engine