Ignition Coil Ballast Resistor Test???

[55 Fargo]

How is the ballast resistor tested, to see if it is in working condition and functioning?

I tried this test, supplied 12 volts to on terminal, and got a 12 volt reading on the other side of the terminal, does this mean it is garbage, or does the resistor need to heat up, to lower voltage?

I am not sure if my test method was correct, or not....Fred

[Greenbomb]

Check it with an ohmmeter. Not sure what the resistance should be, but it should be either good or bad. Not much in between, unless there is corrosion on it.

[Dodgeb4ya]

1.4 ohms

[oldodge41]

If you put 12v in and got 12v out it is probably ok since a break in the resistor would yield 12v in and 0v out. Without a load on the resistor it acts just like a wire. You could do a resistance test because it could be shorted giving you 12v on each end but in my experience they break to an open condition when bad.

[suntennis]

The function of the resister is to reduce the input voltage from 12 to 6 volts. When these resisters fail, sometimes they will only after being heated up. Years ago I had a Valient that would almost die after driving about 20 minutes on a freeway caused by the resister. when replaced, the car ran great for years.

[1941Rick]

The voltage will drop after the ballast heats up...gives a full 12 volt to aid starting then warms up....

[Don Coatney]

The voltage will drop after the ballast heats up...gives a full 12 volt to aid starting then warms up....

That is not the way it works. If there is a 12 volt starting boost it comes from a post of the selenoid. The original 6 volt starter solenoid only has 3 posts. I installad a Ford 4 post solenoid. In the picture below the post without a wire connected is "hot" with 12 volts only when the solenoid is energised. After this picture was taken I ran a wire from this post to the power side of the coil. By doing so I have by passed the resistor when the starter is spinning thus supplying a full 12 volts to the coil. The ballast resistor reduces voltage the instant it is powered up and current flows.

[55 Fargo]

Thanx all, tested ballast today with Ohm meter, and get 1.4, but the spade terminals need a good cleaning.

The bottom line is this, the truck starter motor, does not use a solenoid switch, nor does it utilize a starter button, you simply have direct power to starter from battery, and the moment you push the foot pedal, the starter will crank the engine.

The ignition switch function simply turns the power on to the coil, to allow engine to fire or shut down.

Now in order to have 12 volts to the coil, just wile engine is cranking, need to install a solenoid switch, or run a hot wire to the coil from igntion switch crank postion, to provide a full 12 volts to the coil. This I would have to hold the key in the crank postion, while I hit the starter pedal, then once engine starts,let key position slide back to the on position, to allow current to flow through ballast resistor to the coil, I might need a diode in that set-up, to stop current from flowing back to the ballast, while in the starter crank mode. Installing a solenoid switch might work, but would still have to hold the key on crank position, while hitting starter pedal with foot, till she fires.

Now what in the world did Dodge do for the 1956 or 1957 trucks wih 12 volt set-ups, when they used the foot pedal starters???

I think most of yall, are thinking with the cars, that used solenoid switches, and the starter buttons.

Can I not just run the current throught the ballast, even for start up, or would it make it difficult to fire???????

[Don Coatney]

Fred;

It is not necessary to start on 12 volts. All 6 volt cars do not use 12 volts. I ran for a long time before I added the 12 volt start option. I added it because the option was there to do so with the new 12 volt solenoid I bought. You do not need to do anything unless you want to.

[55 Fargo]

Fred;

It is not necessary to start on 12 volts. All 6 volt cars do not use 12 volts. I ran for a long time before I added the 12 volt start option. I added it because the option was there to do so with the new 12 volt solenoid I bought. You do not need to do anything unless you want to.

Okay, but the engine and operating system is and will be 12 volts, this includes the starter and alt, lights etc.

So if I utilize the current throught he ballast on start up, and running mode, it will be okay.

I may wire in a by-pass circuit later, to allow my system to function as yours does. But for now I need to kow the way I have it set-up, that she will start, and of course will run, as I have described.......thanx Don

[Dodgeb4ya]

Here is a pasenger wiring diagram for 56 dodge cars.

[55 Fargo]

Thanx Bob, just hooked up a small 12 volt battery to 1 contact on the ballast, test meter to the other, and test meter ground to battery ground, and got 13 volts.

So this ballast is not resisting any voltage, and not dropping the voltage. I would have thought, the ballast would not carry any current, if it was toast, but i guess it still is, but not dropping any voltage. Does this make sense.......

OOPS, in order to test voltage and amperage drop, you need to wire the ballast resistor, to a power source and muiltmeter, to ignition coil, done in series. This will give you the volage drop, and amperage draw.

My ballast resistor, has an ohm reading of about 1.4, so should be okay, sorry about all the hysteria around this, a learning curve for me too, the more I learn, the better I like it.................LOL

Edited November 14, 2011 by Rockwood

[suntennis]

On most resisters, if current passes thru it, it should be working OK and give designed resistance. As I mentioned before, there was a failure that occured with my resister after it had heated up. After the resister cooled down, it would seem to work until it heated up again.

There is something wrong with your test result because you should see a voltage drop thru the resister. I just did a similar test for both of us with a spare coil which also has a resistance of 1.4 ohm. For some reason I saw a slight voltage drop from the battery to the coil which was probably due to resistance of test wire. The voltage on one side of the coil was was just under 6 volts and voltage on the other side was under 1 volt. The coil was not attached to the car and small test wire was used on each side of the coil. Hope this helps. If your resister checks out at 1.4 ohms, it is probably good.

[1941Rick]

Here is an article from an Imperial site......

Purpose of Ballast Resistors from Brooks:

When the engine is running, you can get by fine with a lot less current at the points. That's the purpose of the ballast resistor. If the points were to receive full battery current/voltage at all times, they would only last a few hundred miles before needing replacement.

At the time of cranking (when the starter is operating), a separate wire gives the points the full 12 volts, bypassing the ballast resistor. When you release the key from "start" to "on", all the power to the points now has to flow thru the ballast resistor, preserving the points.

So that's its purpose....for those curious. And I know I'm kinda mixing volts/amps in the above....which isn't fair....but you get the idea.

Addition from Bob:

Let's be clear that there is no separate wire on the early models. The points get the current directly through the ballast. In order to provide the full 12 volts during a cold start, the ballast is also cold and has nil resistance. As the ballast heats up (some of them get VERY hot!) the resistance gradually climbs up to 1.5 th 1.9 ohms thus reducing current to the points.

[Plymouthy Adams]

Bobs addition should apply to GM type coils with internal resistor...for those folks running 12 volts...DO NOT install this coil if remaining on 6 volt...only when going to 12 volt sytems do you use a resistor...best overall approach is to use a coil for external resistor only, that way...the coil and resistor can be tested and changed as needed should one or the other fail..

[55 Fargo]

Bobs addition should apply to GM type coils with internal resistor...for those folks running 12 volts...DO NOT install this coil if remaining on 6 volt...only when going to 12 volt sytems do you use a resistor...best overall approach is to use a coil for external resistor only, that way...the coil and resistor can be tested and changed as needed should one or the other fail..

Okay, thats what I am doing, but am using a 6 volt coil, with the external resitor, and 12 volt supply. Can the older type 6 volt coil handle this, I would think so, if the circuit only provides 12 volts through the resistor fo ra short time.....

[55 Fargo]

1 other tidbit, as my distributor had been out for a while, I popped her in, pulled # 1cyl sparkplug, spun engine over by hand til I heard a whoosh of air. I then see the rotor at 1 oclock position in diz, pulled diz, rotated 180 degrees to 7 oclock position, she slides back in.

Is that the right way to do it, or should the diz be out when finding #1 cyl TDC......

[Plymouthy Adams]

Okay, thats what I am doing, but am using a 6 volt coil, with the external resitor, and 12 volt supply. Can the older type 6 volt coil handle this, I would think so, if the circuit only provides 12 volts through the resistor fo ra short time.....

the six volt coil and the 12 volt with external resistor is basically the same thing..when upgrading to 12 volt it is the value of the resistor accompanied with the number of cylinders and even top speed if racing that you will effectively chose the correct dropping resistor to ensure proper current flow for your application..(the ole full stauraion)...using a known good stock original 6 volt coil with the right resistor is adequate..as for most parts none of these old hoopies are really going to see race conditions, match the value of the resistor to the value of the primary of the coil selected and you should not have a problem..

[55 Fargo]

Here are 3 pics of the ignition set-up.

Yes all is used except for the wire, the distributor cap is almost new as is the point rotor and condensor.

The coil is from an early 50s Ford 2 ton it tested at 1.8 to 2 Ohms, the high tension wires are used, the ballast resistor was used on this engine, prior to its being parked for 6 years.

The alt wire is only 12 gauge, will change this to 8 or 10 gauge for permanent use.

The plastic fuel filter is for temp use only, as I want to see whats going on.

[RobertKB]

1 other tidbit, as my distributor had been out for a while, I popped her in, pulled # 1cyl sparkplug, spun engine over by hand til I heard a whoosh of air. I then see the rotor at 1 oclock position in diz, pulled diz, rotated 180 degrees to 7 oclock position, she slides back in.

Is that the right way to do it, or should the diz be out when finding #1 cyl TDC......

You have to be sure that the piston is on the compression stroke and not the exhaust. You will get a rush of air out of the spark plug hole on either stroke. That will determine the wire position on the distributor.

[1941Rick]

This is what I did when i switched to 12v.....put on a 12v coil with external ballast.

[55 Fargo]

You have to be sure that the piston is on the compression stroke and not the exhaust. You will get a rush of air out of the spark plug hole on either stroke. That will determine the wire position on the distributor.

will find out

[55 Fargo]

This is what I did when i switched to 12v.....put on a 12v coil with external ballast.

12 v coil with external ballast resister and 6 volt coil, seems to be 1 in the same....

[55 Fargo]

When a distributor has been removed, and the engine has been cranked over, but nothing taken apart, like timing chain or sprockets etc.

Does the distributor, not go back in only 2 positions 180 degree opposite. So if you place the cyl 1 to TDC, and the rotor is point to 7 oclock, and the #1 high tension wire starts there, should it not be correct, could it only be out 180 degrees at that point if in wrong?

[Robert Horne]

Here is a pasenger wiring diagram for 56 dodge cars.

In the 56 Dodge diagram, the ballast resistor appears to be connected in

between the distributer and coil.