Charging trouble

[Infinitrium]

This is the 2nd time in one day that My battery has run down without the battery light in the dash coming on. I looked at the wires on the regulator on the alt and they seem to be a bit loose, the blue wire doesn't look good, and there was a single thin red wire with a plastic connector that was dangling that looks like it belongs on the B+ terminal. I wiggled the wires around and reconnected that thin red wire but it didn't help any. What else should I check?

[Vincent Waldon]

Does the alternator warning light come on when you turn the key to "on" ?

I ask because if the answer is "no" then you likely have a wiring issue preventing the alternator from receiving the excitation voltage it needs to get started.  No excitation voltage -> no alternator output -> no charging -> dead battery.

In other words, the warning light is actually an key part of the charging circuit and must function properly for the entire system to work.

[55mpg06]

Greetings

What type of VW do you have? Diesel I persume? probably 1985-1990?
Have you had a problem like this before?

I believe the wire with the plastic connector you connected is your output for your tachometer. The small wire close to the big wire is your alternator warning light. It is ment to light when there is a problem with the alternator charging the battery (the output of the alternator.)

The big wire goes from the alternator to the starter and from the starter to the battery to charge it. You could check the connection (a bolt) on the starter for corrosion or it being loose (REMEMBER TO DISCONNECT THE BATTERY FIRST or else if the wrench or your watch hits ANY metal it will spark and you will have a bigger jolt that 4 expressos to go)

As for why your battery is dead? Twice in one day is quite bad. Well a diesel dosen't use much power to run as there is no sparkplugs. So either your battery is toast or dry of battery fluid or somthing is using power when the car is not running. I would check your trunklight (the switch can be dirty at times or not be pressed down enough when the lid is down), any reicent additions like driving lights or stereo and or amp. Make sure the addons are truly off not just on standby when the car is off, particulary amps as they can draw alot of power.

That said, after checking these, if you found nothing it would be a good idea to go to a shop and have the battery tested. After that you could get a reputable shop to test your alternator.

Hope this helps

[Infinitrium]

I tried it earlier today. It needed a boost to get started, obviously the battery in my car is flat dead and probably no good now. I connected a voltmeter to the battery cables. At idle it's only putting out 11 volts, but when I rev the engine up it'll jump to 13, then it'll hit 15. Letting the engine fall back to idle speed, the output also falls back to 11. Hm, bad regulator maybe?

[Infinitrium]

I did a quickie repair on the blue wire. I just cut the bad section out and twisted the two ends of the repair wire onto the blue wire and around the terminal on the alternator. I also found another problem. The proper upper bolt for attaching the alternator is missing so I had just stuck another bolt in there. The bolt I stuck in there isn't quite the right size but I thought it would work. I can tighten that bolt as hard as it will go and the alternator will still slip down and get loose and that appears to be causing some of my charging trouble. If I pull upwards on the alternator to put some tension in the alt belt, the voltage output jumps from around 10.5 V to 14.5 or 15 V. I guess now I will have to get a proper bolt. Is it a specific size I can get at a hardware store or is it something I will have to go to a VW garage to get?

[Infinitrium]

Noticed something else just a little while ago. There's a bracket towards the bottom of the alternator that bolts into the block, and this bracket wasn't attached to anything, it was just dancing around. Reattached that, the bottom adjuster bolt and the top bracket bolt and the belt it good and tight. Running at idle it's putting out 13.6 volts.