TheSamba.com :: View topic - Do you need the alternator light for the charging system?

Sun Sep 20, 2009 8:40 am

Ok my marathon two weeks of getting my car up and running is over. The bug is complete except for a few issues... I took the car out for its maiden voyage and stopped for gas 5 miles from my home. The battery was toast. I had a few people help me push start the ol girl and I drove it straight home.

Long story short...

I rewired my bug with an aftermarket wiring kit that I rigged up for a VW. Everything works except the charging system. I remember something about the idiot light being required for the charging system. I have a flat dash and the old speedo was pitched for a VDO setup. No idiot light.

I have the blue wire off of the regulator coiled up in case it was actually needed. Do i need to set up a dummy light under the rear seat to complete the system?

Please help me!!

Sun Sep 20, 2009 8:44 am

Quote: Do i need to set up a dummy light under the rear seat to complete the system?

Or a load resistor. The bulb way would be easier.

Sun Sep 20, 2009 8:50 am

Do I just hook it to the blue wire? And ground it obviously...

Sun Sep 20, 2009 9:12 am

cory43767 wrote: Do I just hook it to the blue wire? And ground it obviously...

NO! Positive 12v on one side, blue wire on other.

Sun Sep 20, 2009 10:12 am

And it would help you to mount the light on the dash so you can see if your charging sys is working.The 12v to the light should come from the ing sw when turned on .The blue wire on my alt plugs unto a 1/4 in spade on the alt.
LOL Mike

Sun Sep 20, 2009 11:36 am

Technically, an idiot light is not required for a generator system to work. A generator does not need the exciter field like an alternator. It is manditory is you are running an alt however.

Sun Sep 20, 2009 2:39 pm

It's good to have the light no matter what. If it comes on while driving, either the charging system quit, which may be a $200 repair, or the fan belt broke, which could be a $1500 repair, especially if you don't have the light. Your choice.

Sun Sep 20, 2009 4:14 pm

Thank you for all your help. I have been in the garage all day replacing tranny mounts. Oh what fun that was! I think I will hide it under the dash so it is out of sight from the naked eye, but will light up to warn me. I don't want to interupt my clean dash.

Sun Sep 20, 2009 5:42 pm

You could add a buzzer as some people do due to the importance of knowing if your belt breaks,

From Speedy Jim's

Also with lights left on warning

jim

Sun Sep 20, 2009 6:54 pm

nice dash!

Sun Sep 20, 2009 9:17 pm

Are those lights above the gauges? Maybe use them but remember the light isn't grounded.

[/quote]

Sun Sep 20, 2009 10:41 pm

dirtkeeper wrote: nice dash!
Hell...nice car !

Mon Sep 21, 2009 5:22 am

Thank you everyone!! Jamesdagg I like your sugestion of the buzzer. That is just slick!! I will definitely be doing that this week!

Tue Oct 27, 2009 5:23 am

OK I am still having charging issues. I have wired in a buzzer, didn't help. I thought maybe the alternator may be bad, so I took it to my trusty local Auto Electric shop. They checked the Alternator and the voltage regulator. Both are working good. I have checked my wiring from the alternator to the regulator. Everything is hooked up properly with good connection. I replaced the buzzer with a peanut bulb, hoping to mimick the stock speedo idiot light... still nothing! I am just running off battery voltage!

Ok a couple questions... In the vw-resources.com help section they talk about how the bulb is grounded through the base and then the blue wire hooked up to one post and ignition hot to the orther. WTF? It is only a single filament bulb. How can it have three connections. I am very confused!!! I feel like Lewis Black getting ready to burst a blood vessel!! Somebody please explain this to me! Here is the quote from the website and the website is at the bottom.

"The system is very simple, but it's absolutely critical that you get it right. The (D+) terminal on the alternator MUST connect to a functioning warning light in the instrument cluster. There should be just one wire (blue) from the (D+) connector on the alternator to the button on the bottom of the normal indicator light in the dash. The dash light is also wired from the (D+) (Blue) to ignition terminal #15 on the coil, which in turn is connected to the positive (+) post on the battery (Black). There is no ground wire on the light; the body of the bulb is connected to ground via the light holder (which also provides the ground connection for the other dash lights as well.) The three bulbs (ALT/OIL/TURN) all have a common connection in the socket which goes to ignition terminal #15 on the coil (which receives power from the (+) post on the battery by way of the ignition switch)."

http://www.vw-resource.com/alternator_wiring.html#alt
By the way, a very good site for help!

Tue Oct 27, 2009 6:22 am

cory43767 wrote:

There is no ground wire on the light; the body of the bulb is connected to ground via the light holder (which also provides the ground connection for the other dash lights as well.) The three bulbs (ALT/OIL/TURN) all have a common connection in the socket which goes to ignition terminal #15 on the coil (which receives power from the (+) post on the battery by way of the ignition switch)."

!

are saying that the lights are getting ground through the holder? this is the problem. the light should only get ground from the D+ terminal til the engine starts. then the D+ changes polarity and the light goes out. the oil sensor light works the same way except the sensor switch break from ground when the oil pressure builds. you need a light that does not ground through the housing. i use simple 14 volt socket and bulbs like this one on my baja.

Tue Oct 27, 2009 6:51 am

Ok I installed a peanut bulb holder and a peanut bulb, just like I was told and nothing. The one lead is hooked to the blue wire from the alternator and the other is hooked to ignition hot. Still nothing? Battery voltage only.

I am wondering if the local auto electric shop didn't test properly? I am frustrated with this problem!!! I am trying to keep the ol' motorola alternator, but if I cant get this issue worked out I am going to a one wire alternator!

Tue Oct 27, 2009 10:00 am

did the light come on before you started the car? did it go off after you started the car? in fact, you may have a bad alternator. try something just for grins, run a wire from the positive side of coil to a light and to the D+ terminal. when you turn on the key the light should come on. then start the car and see if the light goes out and the alternator is charging. maybe somewhere along the line from front to back a wire went bad.

Tue Oct 27, 2009 10:06 am

I have done that with a test light with now change. I think the bulb in my test light is about the size of the indicator light. I will tear into it tonight when I get off work.

Are the motorola alternators worth all this hassle or should I go ahead and come up with the cash for a one wire??

Thu Oct 29, 2009 7:19 am

Ok I checked all the connections again and the crimp that I made on the dummy light wasn't making good contact. Fixed now! It still amazes me that the Idiot Light is a critical part of the charging system! Gotta love German Engineering! Freakin Brilliant!

Thanks again for all your help!

Thu Oct 29, 2009 7:40 am

cory43767 wrote: It still amazes me that the Idiot Light is a critical part of the charging system! Gotta love German Engineering! Freakin Brilliant!

Um...every alternator in every car in the entire world works the same. They need an initial seed current to get the rotor windings excited. Once the engine is turning the alternator, the alternator can feed the windings itself, but it has to have something to start with. And since a single wire can supply the warning light and also supply the necessary seed current, in terms of number of wires it's a simple, elegant solution. It's a compromise that allows alternators to be very efficient and light and simple to make, since they contain the very minimum of wiring and no (big heavy) magnetic materials.