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I have a '66 Beetle, converted to 12V, with a Bosch internal regulated Alternator that's less the two years old. Lately I've been noticing that my Gen light glows when driving at night with the lights on. It even glows a bit with the lights off, but less. This tells me that it's probably glowing in the daytime too, I just can't see it. Anyway, here's the weird part. It doesn't glow at a constant level. It gets brighter and dimmer. Sitting at a stoplight with the engine idling, it pulses like it's hooked up to a stereo that's pumping out some bass pounding tunes, only I have no stereo. If I rev the engine up a little it gets brighter. I've checked the voltage at the battery terminals and at the fusebox with the engine running. I'm getting about a half-volt drop from the battery to the fusebox. Here's what voltages I'm seeing:

With engine running and nothing on: 13.8 at battery, 13.4 at fusebox
With engine running and lights on: 13.5 at battery, 12.8 at fusebox

Stepping on the brakes with the lights on and engine running drops the voltage at the fusebox down to 12.

Any ideas?

Follow up questions..

What happens when it's night and you turn off the accessories?

Still glows a bit. Around 13.4V at the fusebox.

Meaning does it get brighter when accessories are turned on.. then goes dim when off.

T.

Yes, brighter with accessories on. It also gets brighter when rpms increase above idle, but only slightly.

If you have an alternator and the lights pulse, it usually indicates that one of the diodes have crapped out. I'd start by getting the alternator tested and probably rebuilt.

It doesn't pulse consistently. It's more like a random variation of intensity.

OK, then it's probably not a diode issue. That would be a constant pulsing. I just realized that you said it glowed brighter when the RPMs were increased. Double check that the voltage regulator is wired correctly.

I looked around for a way to test a diode in an alternator and here is what I came up with:
The exact charging voltage will vary according to the battery’s state of charge, the load on the vehicle’s electrical system and the temperature. The lower the temperature, the higher the charging voltage, and the higher the temperature, the lower the charging voltage. The "normal" charging voltage on a typical application might be 13.9-15.1 volts at 77° F. But at -20° F, the charging voltage might be 14.9-15.8 volts. On a hot engine on a hot day, the normal charging voltage might drop to 13.5-14.3 volts.
One way to check the integrity of the alternator and diodes on a Bosch alternator is to check the voltage readings at the D+ (blue wire) terminal and B+ terminal. The voltage reading should be the same at both terminals. A difference of more than one volt would indicate faulty diodes and the need to replace the alternator.

Info from http://www.babcox.com/editorial/us/us20310.htm

It sounds more like you have unwanted resistance in your system, somewhere between B+ and your fuseblock.

Your GEN light works based on the differnece of potential voltage from both the voltage at the front of the vehicle (fuseblock, GEN light) and the voltage that the alternator is producing (B+). When the car is idling the GEN light dims because the output voltage of the alternator is slightly less and so the voltage difference is less. As RPM's increase, so does the output of the alternator, and the voltage difference increases, thus making the GEN light glow brighter.

I would check for voltage drop at accessible points from B+ on your alternator all the way to the fuseblock to try and locate the unwanted resistance in your charging system.

I had the same problem awhile back, and it ended up being too much resistance in a few of the spade connections in my 30+ year old wiring.

Yah, I thought it might be something like that. I will do some more investigating. Thanx.

My bug behave the same way; "It doesn't pulse consistently. It's more like a random variation of intensity." But my problem is solved now! What I did was to clean-up all electrical contact point, the fuse holder copper strip, use a plier and pinch all wire crimp for a tighter grip, sand all crimp terminals, solder all crimped wire to the crimp, check all wires joint and solder those that are just twisted together, battey terminals clamp changed and terminals/wires cleaned.

Volla!... its like magic--I am amaze at how the car seem to be much more alive and the idling speed increase by 180 RPM without me doing anything to the carb--I am wondering why that so--due to better conductivity of electrons?

My bug behave the same way; "It doesn't pulse consistently. It's more like a random variation of intensity." But my problem is solved now! What I did was to clean-up all electrical contact point, the fuse holder copper strip, use a pliers and pinch all wire crimp for a tighter grip, sand all crimp terminals, solder all crimped wire to the crimp, check all wires joint and solder those that are just twisted together, battery terminals clamp changed and terminals/wires cleaned.

Volla!... Its like magic--I am amaze at how the car seems to be much more alive and the idling speed increase by 180 RPM without me doing anything to the carb--I am wondering why that so--due to better conductivity of electrons?

I, too, have fixed my problems. In my case I moved my headlights onto a relay, which pulls power directly from the battery down a dedicated 10 gauge wire. Presto, no more glowing gen light, and my headlights are brighter too. I think the stock wiring harness was just a little inadequate for my H4s.

66beetle wrote:I, too, have fixed my problems. In my case I moved my headlights onto a relay, which pulls power directly from the battery down a dedicated 10 gauge wire. Presto, no more glowing gen light, and my headlights are brighter too. I think the stock wiring harness was just a little inadequate for my H4s.

Ayep. You would have fried your harness, eventually.