What stops the fire?

[Roadster62]

Just looked at a Model A wiring skematic, and as a clueless electrical terrorfied body guy have two questions. There is a cable from the battery to starter, and a small yellow wire from the same starter connection. This yellow wire powers EVERYTHING IN THE CAR as I understand it. When you try to start the car an unknown to me amount of jigawats flow through the starter cable, what prevents that yellow wire from busting into flame under the same load?

 

[stouchton]

The yellow wire does not start the car, the battery cable supplies the juice to start the car.

The yellow wire supplies the ignition (coil), lights, horn and also serves as the return path for charging.

Yellow wire carries 25 amps or less (worst case by my calculation)

 

[jrelliott]

The yellow wire on the starter is to the generator and the rest of the vehicle. Suppliers make a fuseholder to put in series with that connecton and a 30A fuse for the holder. The current going to the rest of the vehicle is small compared to the current going to the starter. I personally like the idea of the fuse. Others may say not original, but for safety a fuse.

 

[REdington]

If I understand your question right, the battery cable handles the power for the starter. The ground to the block makes the complete circuit for the starter and the yellow wire powers everything else for the car.

Rodney

 

[Mike V. Florida]

if i understand your question right, the battery cable handles the power for the starter. The ground to the block makes the complete circuit for the starter and the yellow wire powers everything else for the car.

Rodney

yup

 

[Roadster62]

Yes, but the small yellow wire is attached to that battery cable, so why isn't it being fried?

If I understand your question right, the battery cable handles the power for the starter. The ground to the block makes the complete circuit for the starter and the yellow wire powers everything else for the car.

Rodney

 

[Purdy Swoft]

Not tring to be a smart azz, you don't have to completely understand it to enjoy it. If there is a problem with the wiring, just connect the new wiring harnesses as shown in the diagram and it should be good to go. When I use to make my own wiring harnesses, I used a larger wire in that location.

 

[Charlie Stephens]

Yes, but the small yellow wire is attached to that battery cable, so why isn't it being fried?

The only current through the small wire is what is being pulled by the things connected to it (horn, lights, etc). The small wire is not connected to the starter and therefore there is not that large amount of current being pulled through the small wire. If you tried to pull as much current through it as dead short or the starter takes you would fry the small wire.

Charlie Stephens

 

[REdington]

I'm not in anyway a electronic nut but I will try to explain it. When you push the starter pedal, it make a complete circuit from the battery cable from the battery to the starter. The other side of the battery has a cable that goes to the ground on your car. The starter is grounded to the engine through the bolts and connection to the bell housing. These two cable take all the amps to turn the starter.
The yellow wire could be hooked up directly to the battery and it would still work. The only time the yellow wire would get hot and burn is when it is drawing more amps that it can carry, like if it were to get shorted out on a grounded part somewhere.

Rodney

 

[P.S.]

I'll attempt to provide a useful answer and hopefully be able to help. My apologies in advance if this isn't helpful.

In order for DC current to flow through a wire, there has to be a current "loop". In other words, there has to be a complete circle, like driving around the block. There is a + and a - terminal on the battery. Current flows from the - terminal to the + terminal to create a circuit.

For example (in a positive ground stock system), to illuminate your dash light, current flows from the - terminal of the battery, through the large cable to the starter, through the yellow wire you mentioned, through the light switch, through the light filaments, through the light holder, through the body, through the chassis, and back to the battery + terminal.

Well, let's look at the current flow for the starter itself when starting the car- Current flows from the battery - terminal through the start switch, through the starter motor, through the starter case to the motor, through the chassis, and back to the battery + terminal. NOWHERE in that loop is the yellow wire included, thus no current flowing through the yellow wire to start the car. The only current flowing through the yellow wire if for the car's other electrical stuff, like the lights, ignition, etc. That current is very low compared to the starter current.

 

[Ed H.]

It is the same on many of todays cars. They put a feed wire under the starter cable to feed the rest of the car.
Never had an issue with the feed wire causing problems unless as stated above the wire is overloaded.

 

[Mike V. Florida]

This may help

 

[Roadster62]

For the sake of discussion I'll believe the above, another question is direction. This is about Model A's I'm sure every other car is different and don't want to go there. Is the electricity in an Model A PUSHED or PULLED? Can the direction be traced? The ground symbol has always confused me, it just looks like it is a discarded unwanted item even though it is needed. Bob

 

[REdington]

There is two basic types of electric current. DC (direct current) that uses a battery and AC (alternating current) that we use in houses. I'm pretty sure DC flows from the + (positive) to - (negative) .

Rodney

 

[Roadster62]

Still over my head. Could someone draw arrows on an A skematic to show the path/direction?

There is two basic types of electric current. DC (direct current) that uses a battery and AC (alternating current) that we use in houses. I'm pretty sure DC flows from the + (positive) to - (negative) .

Rodney

 

[Roadster62]

If so, on a Model A with a positive ground hookup the electricty is sucked out of the frame like water gets sucked up the roots of a tree?

There is two basic types of electric current. DC (direct current) that uses a battery and AC (alternating current) that we use in houses. I'm pretty sure DC flows from the + (positive) to - (negative) .

Rodney

 

[P.S.]

There is two basic types of electric current. DC (direct current) that uses a battery and AC (alternating current) that we use in houses. I'm pretty sure DC flows from the + (positive) to - (negative) .

Rodney

DC current flows from (out of) the battery anode ("-") to (in to) the battery cathode ("+") terminals.

In a Model A with the stock positive ground, the negative ("-") side is the "hot" and the positive ("+") side is the "ground". Current flows from the battery negative terminal, through the electrical system and returns through the chassis to the positive terminal.

 

[REdington]

Here is a quick drawing

Rodney

 

[Willie Krash]

R62, I would not concern myself with pushing/pulling. Think of a light switch. When you close the switch current will flow to the light even tho' its on the same circuit breaker as other devices. When trouble shooting remember electricity will follow the easiest path to ground, completes the loop. Short of like a sewer pipe.
Positive ground or negative. That is a non-technical answer but for us lay people it works.

 

[Roadster62]

P.S and REdington, may be correct I just don't know which one is. Bob