battery draining power?

[jarmchairpilot]

Having electrical gremlins.Last week after a night time drive of 20 miles,I arrived at my destination and switched lights and ignition off.1 minute later I went out to move the bug a few yards,only to hear the starter struggle to make even 1 turn and the two red(ignition and gen)lights came on dimmly for a second and faded out.I brought my battery(6 month old,seems fine) to a nearby garage and had it charged overnight.The next day with charged battery,the bug fired up no problem.
The problem is I dont know what went wrong in the first place.
I noticed while driving at night the headlights seemed at times to kind of pulse,I mean they would seem to get stronger for a few minutes then drop power.
How can I tell if the problem is something causing a drain on the battery,or if the charging circuit is at fault.My generator is only a year old,same as my starter motor and both are expensive Bosch quality items.
My bug is a 72 Standard 1200.Thanks.

[Luft kühl]

[Cusser]

Yeah, that's called parasitic drain, so look it up.

Sometimes, alternators are the culprit.
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297

[jarmchairpilot]

I tested for battery drain,did,nt find any.

[Luft kühl]

There are two other things that you can try.

Have the battery load tested.

Test the charging system. http://www.speedyjim.net/htm/gen.htm

[Cusser]

Test for charging system actually operating.

Disconnect battery overnight or a few days, see if it starts. A good battery will be fine to start a vehicle after several months (like in my 2004 Frontier).
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1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297

[dirtkeeper]

[jarmchairpilot]

I found a dodgy connection at the voltage regulator on the thin red wire that comes from the battery,this was causing my battery to stop charging while driving.I still have a problem that is causing the battery to drain after the bug is parked up.My no.1 fuse is blown,this is the one that should provide power to the two small front parking lights.

[Luft kühl]

In addition to the two gray wires for the front parking lights, there should also be a red/gray wire connected to fuse #1 that powers the license plate light.

Disconnect all three wires from the fuse, switch the parking lights on, and reconnect the wires one at a time until the fuse blows. You will now know which circuit has the problem.

[jarmchairpilot]

I had to replace the voltage generator,I guess the original lasted 40 years,so I hope the stock Bosch replacement is as good!At least my battery has survived in good condition.