Pulsing lights

[wyopel]

ALL the lights in my B4 have started pulsing NOT flickering but pulsing between bright and not bright at a frequency of about twice per second. When I say all the lights I mean headlights, cluster lights, dome lights, everything.

All grounds are checked and clean, cluster was repaired (new caps) and is working fine. When the car is not running and lights are on with battery power only, they do not pulse. Alternator seems to be charging, but voltage coming to battery pulses between 14 and 14.9v.

I saw a couple of other threads describing something similar but no solutions. These symptoms make me think it is the alternator or a voltage regulator somewhere not working right.

What do you all think?

 

[Vince Waldon]

Undervoltages can be a bunch of different things but overvoltages pretty much point straight to the regulator.

The voltage regulator is responsible for making sure the alternator puts out a smooth 14V... pulsing between 14 to almost 15 means it's time for a new one.

That said... worth pulling the regulator and examining the slip rings as well... might be worth replacing the alternator completely rather than going half-way with a new regulator if the rings are worn as well. Worn rings/brushes would cause voltage drops, not overages, but a new reg gets you 1/3 of the way to a new alternator, cost-wise., and I hate buying a new reg only to have to buy a whole alternator a few months down the road.

 

[wyopel]

Thanks. That's what I figured. I have an spare alternator. I'll pop that on and see what happens.

 

[Mongler98]

either worn brushes, and or regulator/ rectifier.
either way, rebuild yours or replace with OEM

 

[Mozambiquer]

I second alternator problems. These bosch alternators often wear the slip rings out, and then it will pulse like that. If you need any parts, let me know, I can get them for you.

 

[KLXD]

Seems to me a rhythmic pulsing would be the regulator rather than the brushes but they are one assembly, no? So swap the assembly rather than the whole alternator to check.

When mine went bad I just got the light. Temporary fix was to pull on the brushes to stretch the preload out of the bent wires. Worked fin for a week or two while I ordered new brushes and slip ring. So maybe try that. Mine Had grooves almost 1/8" deep.

 

[Mozambiquer]

Seems to me a rhythmic pulsing would be the regulator rather than the brushes but they are one assembly, no? So swap the assembly rather than the whole alternator to check.

When mine went bad I just got the light. Temporary fix was to pull on the brushes to stretch the preload out of the bent wires. Worked fin for a week or two while I ordered new brushes and slip ring. So maybe try that. Mine Had grooves almost 1/8" deep.

Most often when i see the lights pulsing, it's either caused by a slip ring that's going out, or if its a failing rectifier which allows too much ripple voltage through.

 

[Vince Waldon]

It appears, based on his measurements, that the pulses are over-voltages, not drop-outs.

 

[Mozambiquer]

It appears, based on his measurements, that the pulses are over-voltages, not drop-outs.

I saw that now. I would check the ac ripple voltage next.
It is possibleto have a voltage regulator fail high, but that is not normal, and if it does, that is normally indicative of an aftermarket regulator.
Another possibility would be poor grounds causing the regulator to see low voltage and ramp up production.

 

[wyopel]

Definitely over-voltages. Never dropping below 14v and not going over 15v. I swapped the alternator with a spare I had. The problem is gone. The bad one was not a Bosch. I'm not sure it is worth rebuilding.

 

[Mozambiquer]

Definitely over-voltages. Never dropping below 14v and not going over 15v. I swapped the alternator with a spare I had. The problem is gone. The bad one was not a Bosch. I'm not sure it is worth rebuilding.

That's not surprising. I've seen so many aftermarket starters and alternators fail prematurely, and many that are bad out of the box. It's disgusting!

 

[Abacus]

That’s why I have them rebuilt now, too much new trash out there, even with the ‘lifetime’ guarantee.