The parts list for my 60 f100 showes a ballest resistor wire rather than a plug in block. Does anyone know where that wire runs and connects to?

 

Howdy,


The Ballast Resistor is simply a series resistor that goes in the A+ (12V) power wire going to your ignition coil so that during normal running the coil only "sees" about 6v dc. IF you continuously ran 12v to a 6v coil it could eventually overheat.

The Ballast Resistor is bypassed only when the starting motor is powered so as to provide 12v to your coil and maximum spark for starting.

When you release the key (to RUN), the resistor is back in the picture.

Most automotive coils installed with a ballast resistor are 6v coils.

If you look at the simple diagram below, the ballast resistor would go between the battery and + side of the coil.

It would wired so that when the key is turned to START, it would short across the resistor so that it would be effectively bypassed, so the coil would get the full battery voltage during cranking.

When you release the key, the "short" across the resistor would be removed and it would drop the voltage to the coil back to approx 6v for continuous running....


Some people use 12v coils nowadays making the Ballast Resistor unnecessary.

 

OK that helps some. Although since my 60 uses a 12 volt system I'm a little confused about the 12 v dropping down to 6v thing. The diagram was a big help though. Now I just need to run a contenuity test to find the other end of the wire coming off of the coil, since it dissapeares into a wiring hearness and then under the dash as it head's toward the ignition switch, and wiring oblivion.

 

That is a problem if you do not have a decent diagram for your wiring system......

Most wiring systems use the power to the starter solenoid (which is activated when you turn the key to "START" to "bypass" the ballast resistor.

They basically run a wire from the hot lead on the starter solenoid to the coil so the coil gets 12v any time the starter solenoid is getting power.

When you release the key, the "regular" (RUN) path of power is from the ignition switch to the ballast resistor then to the coil.

 

Heres another noodler. The replacement resistor wire has male "bullet" connectors at both end's. I cant find any such connectors from the distributor or the starter solenoid. So I'm wondering if the wire is connected to the starter switch and run's under the dash somewhere.

 

If you want to wire that think up like Ford intended, you'll have to either find an OEM service manual or someone that has a similar truck that can show you were it is, or,

Simply install the resistor in series with the ignition power coming from the key. THEN run a separate wire from the starter solenoid that has power on it during starting directly to the "+" terminal on the coil.

This way, when the key is "ON" the power supplied to the coil with be through the resistor. When you crank the starter, power supplied to the coil will be from the solenoid (and the full 12v).

Here's another good description with a picture.... Ignition Systems* A Short Course

 

Great article, thanks. I had another thought [scary]. At the risk of over simplifying the problem, could I install a coil that already has an internal resistor and just ignore the external one?

 

Yes, but dont try using one of the chrome oil filled Pertronix coils. They supposedly have the proper internal resistance, but get very hot in the right conditions and spark stops. I think they are junk. At least that has been my experience.

I run a regular black coil which doesnt have internal resistence, and before it is an inexpensive ceramic ballast resistor ($5.00). Easy install.

There is a nice chrome Pertronix coil on the shelf that could be had by someone.

 

I assume the ceramic resistor is installed in line of the possitive wire going to the coil?

 

Yes, switched power to one side of ballast, and connect other side of ballast to positive terminal of coil. Ask for one for a Ford 12V. Think the resistence is 1.4 ohms, or very close.

 

I also use one of the ceramic resistors with a big yellow Accel "Supercoil." However, after an inconvenient situation, I always carry a spare resistor in the glove box. Along with this, I also use an old Judson "SeeDee" unit, but only as a switch triggered by the points for the coil. This cuts down on the amount of current the points have to handle and makes them last considerably longer. If this SeeDee unit goes bad, it is a simple matter to bypass it and run the motor in a conventional fashion.

Sometimes, it seems counter-intuitive to have a ballast resistor in series with the coil's primary windings. After all, the idea is to have a hot spark, and the more current passing thru the primary windings, the hotter of a spark should be produced.

If you touch one of the external resistors when your engine is idling, you'll note that it can get warm -- sometimes quite warm. The idea here is that when the engine is running slow or idling, there is a lot of current going thru the coil because the points are being held closed for long periods of time. This high current will not only cause the points to arc, but arcing will also occur as the field in the coil collapses, causing an even stronger arc.

What the ballast resistor does is cut that primary current when the engine is running slowly and the points are closed for relatively long periods of time. The resistor heats up and its resistance increases. As the engine speeds up and the primary current drops, the ballast resistor will cool and allow more current to pass thru the primary windings.

The effect of the ballast resistor is to limit the current at slower speeds, so that it remains more constant across the rpm range of the engine.

There are some coils that do have a ballast resistance built into them. If you know that this is the case with one you intend to use, your problem is solved. However, be aware that some cars did not use a separate ballast resistor -- this function was built in to the special coil primary wire, somewhat like resistor spark plug wires.

 

I don't really think this is true.

A ignition coil is simply a transformer with a high "turns ratio" where the "bottom" of both the primary and secondary windings are connected to ground.

A 12v coil is just that. It's a coil with enough resistance in the primary winding to operate directly at 12v. I guess you could say that a 12v coil has the resistor "built-in" but it's not a separate carbon or wire-wound resistor residing inside.....

The primary winding is wound with enough (turns) resistance to provide the correct resistance so the continuous current rating is not exceeded when the points are closed and the primary is powered.

I had an oil filled 12v coil I used on my 57 Ford 292 for many years. I completely eliminated the "ballast" resistor permanently. It never even got warm.

The main downside of using a 12v coil is when your battery is weak.

If you crank the engine with a weak battery, the terminal voltage can get as low as 10v or lower while the starter is operating. Low voltage on a 12v coil can result in a pretty weak spark.

With a 6v coil and an outboard voltage dropping (Ballast) resistor, you would get that same 10v or so directly to the coil because the dropping resistor is switched out of the circuit while cranking.

The result is still a fairly strong spark even though the battery is a little weak.....


It was never a problem for me because I always had a good battery in the car.

 

What would be the effect/result if I put a ceramic ballast in front of the internal resistence Accel coil?

 

OK Ford Ignition wiring diagram... Notice on the starter SOLENOID the "I". When you turn the switch to start, not only does the solenoid activate the starter MOTOR but it BYPASSES the BALLAST resistor. Very simple. Isn't this what the original question was? "Does anyone know where that wire runs and connects to?" Maj. Spoons, I hope that helps you.



Mike to answer your question, you have lower secondary voltage from the coil due to lower voltage to the primary windings in the coil...

 

BTW, That diagram will work on any engine.....



If you have a simple digital or analog volt meter, put it on the + side of the coil and you'll see. It will simply reduce the voltage to the coil.

If that coil requires 12v to produce a hot spark and you only run it with 6 or 8 v on it, it'll just produce a lower voltage spark. It may still be enough "spark" to run the engine though.



Your best bet is to run the right voltage for whatever coil/resistor (or no resistor)combination you're using.