Why does this wire Spark?

[jchochole]

I just got a '28 Sedan and this yellow wire will spark when it touches the alternator post. The car came like this- can anyone help? The car was converted to 12V by previous owner and this little wire shows 12v on a voltmeter. Must be a direct connection to the battery, but why?

Thanks,
Jim

[Bob C]

That wire goes to the ammeter and then to the starter and battery.

Bob

[jchochole]

So, now that I have an alternator on the car, it doesn't seem like it is needed. Like said, it reads 12V on it with a tester.

[Bob C]

I don't see how you are going to keep the battery charged with out that wire hooked up.

[cpf240]

Originally Posted by jchochole

So, now that I have an alternator on the car, it doesn't seem like it is needed. Like said, it reads 12V on it with a tester.

Then how is the alternator supposed to charge the battery?

Those other two wires go to the horn and the light switch...

[JDupuis]

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That wire is used to recharge the battery......show the charge rate. Jeff

[cpf240]

To get back to the original question, has the alternator been taken in and tested? Perhaps the diode trio has failed, and it is shorted.

[Y-Blockhead]

OK, we established that is the charge wire. You didn't mention when it sparked. Does it spark when the engine is not running? (Alternator not turning?).

You shouldn't have a draw on the battery when it is just sitting there. It sounds like you may have a bad diode in the alternator.

[Purdy Swoft]

The wire that connects to the alternator or the cut out if you ran a generator is suppose to be hot . if the battery is 12 volt it will show 12 volt . The alternators that are sold for use on the model A will have a built in voltage regulator that prevents current entering the alternator . when the engine runs and reaches a certain RPM the regulator will allow the alternator to charge back through the hot wire to the ammeter and back to the battery . If a generator is used the cut out will serve the same purpose but won't give voltage regulation. If the ammeter shows a discharge when the engine isn't yrunning there will either be a problem with the alternator or a dead short somewhere in the system . If a generator is osed it will usually indicate stuck points in the cut out .

[Purdy Swoft]

The yellow wire with black tracer is live . If the yellow wire with black tracer isn't connected to the alternator it will spark any time that it is touched to anything that it can ground on including the post on the alternator . It may be hard to understand how the alternator can charge back through a live wire . Thats just the waty that it works .

[jchochole]

Thanks for the help- to answer the good question, I touched the yellow wire to the alternator post and got the spark when the car was off and cold. I didn't want to fry it in case that was an incorrect connection- but it sounds like connecting it is okay?

I am attaching a couple more pics, the alternator is stamped "12VoltNeg" and none of my lighting is connected for some odd reason (guy cut all the wires) so will my wiring handle the 12V system? Haven't checked bulbs yet.

Thanks for the support, guys! I am attaching a pic of my terminal box and horn wire too, since that gets attached to the alternator post, right- So two wires to the alternator then? Even if it sparks?

**I tested the alternator (car not running) with a voltmeter and shows "zero" touching the post and a ground. So, I assume the diode is good then.

Jim

[Purdy Swoft]

It looks like a mess has been made out of the wiring. the best thing that you could do is replacr the wiring harnesses because of what all has been screwed up . there should be a hot yellow wire with black tracer that connects to the alternator. the headlamp and horn wiring would also connect to the alternator . Because I don't know what all else has been screwed up, I don't want to say anything that could cause other problems.

[Tom Wesenberg]

How big is the spark?
Leave the wire off until the problem is fixed, or you'll kill the battery, or even start a fire.

Your lower coolant pipe is the 1930-1 style, rather than the correct 1928-9 one.

[jchochole]

Purdy- yes, there is indeed a hot yellow wire (that's the sparker) that goes to the alternator. Looking at schematics with colors, the wiring looks in order in the terminal. So, just not sure why I am getting a good spark at the alternator post.

[midgetracer]

If you are getting a spark at the alternator post when the engine is not running there is a problem in the alternator.

[pooch]

Is the battery hooked up correctly?

If the alternator is negative earth and the battery is hooked positive earth, I am sure that will cause a spark.

It blows the main fuse on modern cars if you hook up wrong.

[jrelliott]

If it is a single wire alternator, there is a small draw from the battery while the vehicle is turned off. This is the field windings of the alternator. There is very little residual magnetism like in a generator which will induce a voltage when the generator is spun. You need a magnetic field to have the wires cross to induce a voltage. This is the main reason you cannot push start a vehicle with an alternator but can with a generator.

[Will N]

Originally Posted by jchochole

Thanks for the help- to answer the good question, I touched the yellow wire to the alternator post and got the spark when the car was off and cold. I didn't want to fry it in case that was an incorrect connection- but it sounds like connecting it is okay? ...



**I tested the alternator (car not running) with a voltmeter and shows "zero" touching the post and a ground. So, I assume the diode is good then.

Jim

What setting did you have your voltmeter on? You should have it on Continuity. With the wire disconnected, car not running, from the post to ground you should have no continuity.

As others have said, that yellow wire is supposed to be hot. If it's sparking when touching the post, that tells me the post is grounded. It should not be when the alternator isn't spinning and is not putting out current. The diode is an/off switch. It disconnects the circuitry in the alternator until the alternator starts putting out current. I feel that your diode is shot.

[jchochole]

Okay, sounds like I need to take my alternator to a shop to be tested. Thanks, guys!

I checked for continuity and nothing, no noise out of my meter when I went from post to ground.

[jchochole]

I just checked and my battery is hooked up Negative ground, and my alternator is also negative ground.

I've never had an A with a Negative ground, why do guys switch that?