I rebuilt a 300 last winter and I ve finaly got her in the truck.
She cranks good, has fuel in the carb and oil in the gallies so I must have got that right.
The problem is that I cant get no spark out of the coil.not at the coil lead or at the plug wires. She is in an 85 F150 4 spd truck however I went backwards and put contact ingnition in. I got a 68 distributor and matching coil from my local parts store. Theyve never failed me so Im sure its right.

I ran a switched Positive 12v to the hot side of the coil, and a frame ground to the negitive side.
There is a small black wire coming out of the distributor that I attached to the negitive side of the coil like my 292 is wired, is that correct?
Also on my coil it states that an "external resistor required" whats up with that.
since everyone is asking why use contacts Ill state my reason. Apperance. Duraspark is an ugly bundle of wires. If it rruns Ill install Petronix. I want to put it in my 64 F 100 eventualy so the look is of some import.

in a nutshell.

what is the black wire on the distributor?
what is an external resistor? why do I need one? how do I hook it up?

Thanks a million youall helped me alot.

Flip

 

I'm sure their are folks on here smarter than me on this subject but until they post heres what I know. The external resistor reduces the voltage to your points. Your points need 12 volts to start but once running they last much longer if the have about 6 or seven volts max. When you turn your key switch to start on trucks originally equipped with points it bypasses the resistor and sends 12full volts to the points. Then when you release the key to the run position it changes the flow through the resistor to reduce the voltage to prevent the points from burning. You need a wiring diagram to find the correct place in the wiring harness to place the resistor. You can buy a universal resistor (try a early 70's Dodge) and mount it on the firewall. Ford trucks I believe had the resistor made into a section in the wiring harness near the distributor. I hope this helps.

 

Okay, big no no... you cannot run a frame ground to the negative side of the coil. The way a coil works is this: a positive voltage is constantly applied to one side of the primary winding (the "positive"\BATT terminal of the coil). The other end (the "negative"\TACH TEST terminal of the coil) is temporarily grounded for a very short amount of time. A magnetic field builds in the coil, and a very large voltage develops across the secondary winding of the coil. Then the primary winding of the coil is taken open circuit, meaning the ground for the coil is disconnected. This causes the very large secondary voltage on the coil to look for the next best path to ground, which is the spark plug electrode, through the plug gap of air. This is all done in sync by the distributor.

Anyway, here is the point: the negative end of the coil connects to a switched ground source. For a breaker-points ignition system, this is done through the points. The black wire coming out of the distributor is the coil ground. It connects to the negative terminal of the coil. It acts as a "switched ground" for the coil - the distributor takes care of holding this to ground just long enough for the coil to "charge" and then releases it so that it can fire. Your motor is not firing because you are holding the coil to ground 100% of the time and it can't spark.

The distributor grounds through the hold-down bolt. Nothing else goes in\out of the distributor besides that black wire I just mentioned. A small wire inside the distributor grounds the points to the distributor, since the breaker plate moves about a grommet and does not conduct electricity.

As for the "external resistor required" thing - you cannot run 12V straight to the positive terminal of the coil. The primary winding of the coil is rated for 9V. In a stock Ford ignition setup, the positive lead of the coil is actually made through a special length of resistance wire, such that when connected to the positive terminal of the coil, the actual coil voltage is 9V due to resistive division. But wait, it gets even more confusing. When you are cranking the engine to make it start, the entire system voltage drops. So in a stock wiring harness, there is actually a bypass wire to run straight 12V to the positive terminal of the coil, because when the motor is cranking, the battery voltage is closer to 9V than it is to 12V. Once you take the key out of start and back to run, the ignition switch changes the positive terminal lead for the coil back to the resistance wire, so that the coil sees about 9V in both start and run. Clear as mud?

In a nutshell, here is what you need to know:

1. Between running 12V to your coil and holding the negative terminal permanently to ground, you have most likely fried your coil and you need to replace it.

2. Black wire coming out of distributor goes to the negative side of the coil. Nothing else connects to this terminal of the coil.

3. Do not run full 12V to the coil. You need to drop it down to 9V or so. If you cannot do so with a stock Ford harness, automotive supply stores sell resistors for such applications.

You're right that a Duraspark setup is more wires, but it's not all that much. At least upgrade to a Pertronix setup, if anything. Points are a pain and I hardly hear of anyone actually reverting back to points. Get out your feeler gauge...

 

get a better coil that doesn't require a ballast resistor. These are almost always better (rugged, higher secondary voltage) than the $12 NAPA special.

 

thanks is there any way to test my existing coil for servicabiltity? an ohm test or somthing of that nature.
What sould I ask for to get a coil with an internal ballast resistor. Year and make?

 

Yes, there is a resistance check you can do to check the coil. First disconnect the coil. Check the resistance of the primary winding (resistance between the two small positive and negative terminals), and it should be between 0.5 ohm and 1 ohm, or thereabouts. Check the resistance of the secondary winding (resistance between the small positive terminal and the large center terminal) and it should be between 8 K-ohms and 12 K-ohms.

I can't recommend a 12V coil because I haven't used them myself, so someone else will have to. I do know that many performance coils run off 12V, but be aware that you will have to run a larger spark plug gap to compensate for the higher secondary voltage. However, I can guarantee you that for your purposes there is no reason to go for a hotter coil since you're not doing a full-on performance ignition upgrade. A hotter spark is wasted energy because all it takes to ignite the fuel\air mixture is a good blue spark which the stock coil does easily. The only reason to go with the 12V coil in your situation is to avoid using a ballast resistor, but before doing that I would see which route is cheaper.

 

If you feel the need to have a point style distributor you need to stay with the ALL the parts used in that system. You should not use 12 volts to the coil during run mode as the extra current flow will cause the points to burn up fast. Also the condenser (capacitor) will be getting 12 volts not 6 volts as it was designed for. If you get a 12 volt coil with an internal resistance it will start hard (weak spark) as it will be getting a lower voltage during the time the starter is cranking the engine over.

Bottom line is just to wire it the way a point distributor was wired for it to work the best.

The 12 volt source for the coil during cranking comes from the “I” terminal on the starter solenoid. It is the small on next to the big wire that runs to the starter. The starter solenoid should have 2 big and 2 small connections on it.

Your old coil might be good as you didn’t have much “key on time” to heat it up.

 

Good post; although in my experience the points systems only had the 3-terminal solenoid - 2 big lugs and then only one small terminal labeled "S" for the key-start signal. The Duraspark systems have the 4th "I" terminal to send a signal to the Duraspark box so that it knows to retard timing slightly while the engine is cranking. The coil power then comes from the ignition switch - which takes care of switching the coil power between a bypass wire during cranking and then a resistance wire during run time. I'm not saying Ford never used a 4-terminal solenoid on points; I just haven't personally seen one and I don't see a whole lot of reasoning for it since the purpose of the 4th terminal is for Duraspark, as far as I know anyway.

See the following schematic. You can see the bypass wire shorting the resistance wire in start mode. A points system is very similar, except downstream of the negative coil terminal there would just be breaker points, and no Duraspark box or sockets.



Image courtesy of Autozone.