I have a 1978 F-250 that hasn't run since last spring. It had lost all power. I replaced the battery, starter, and starter solenoid. I have now regained power and can turn the engine over, however, there is no spark coming from the coil. I replaced the ignition module, pickup coil, and coil and still no spark. I am really baffled. Using a test light, there is a light at the + coil connection with the key turned to on and a brighter light when turning the engine over. I understand this is the way it should work. Any ideas where to look next?

 

The system ground is the black wire that is grounded inside the distributor. You might check to be sure it is really grounded. If you had a scope, you could put it on the coil neg terminal. You would see +12 pulses as the module fires the coil. You could also disconnect the coil neg and touch a jumper wire from coil neg to ground. You should get a high voltage spark when you remove the jumper.

 

You probably did this already but.... did you check the distributor cap and rotor for corrosion and damage? Also does the rotor turn when you crank over the engine? Did you check for spark out of the coil wire or just at the sparkplugs?

Sparky

 

The rotor turns when cranking the engine. I'm not getting any spark from the coil itself. This is really baffling me.

 

OK you have voltage at the coil with the ignition switch in start and run. So the problem isnt in the + circuit.
You have the rotor turning, so the problem isnt a sheared pin on the dizzy.
You do not have power out of the coil as in a spark.
So 1)a bad coil 2)bad ignition module 3)bad pickup coil in dizzy....but you have changed all these......so next steps....
1)is there voltage to the ignition module to "turn it on" ,should have 12 volts on white wire when cranking over engine and 12 volts on red/blue wire when key is in run.
2)what kind of shape are the wire connectors on the ignition module in? Are they broken, dirty, corroded etc etc....if they are in real bad shape you could actually cut them out and splice the wires together, makes it harder to change modules but illiminates a problem area for bad connections.
3)is the ground connection on the coil ok? It is a green/yellow wire that runs to ignition module.
4)maybe it is time to check the wiring from the module to the coil and from the module to the dizzy for continuity, might have a broken/corroded wire somewhere.
Ignition Module wires
White - 12 volts during engine starting
Red/Blue Stripe - 12 volts when key is in "run"
Green/yellow stripe - to negative terminal of coil
Pink/Blue stripe - to one side of pickup coil in dizzy
Orange/yellow stripe - to other side of pickup coil im dizzy
Black/green stripe - to dizzy ground

Sparky

ps
I hope I got the colors right Also check and make sure the dizzy body has a good ground.

 

Sounds like you know this electrical system quite well. We're going to follow your suggestions this week. Thanks for your help, Sparky. Fortunately, the snow storm fizzled out. I'll keep you updated.

 

Hi Sparky, What is the function of the blue wire (75 module)? I have this hooked up to my 6v Sun distributor tester. It is working with only the red wire hooked to 6v. The white wire is supposed to retard timimg while cranking, correct? Regards, Mike

 

Well I am no expert on this system, but I think I have it figured out fairly well
As far as I can tell the blue wire on the 75 is used instead of a white wire and is hooked to a 12 volt source that is powered when the key is in "start". I have been told before, and it does make sense, that this circuit is to retard the timing for easier starts.
My diagrams show no white wire for the 75-77 systems and there are a few differences in where the red/blue wire gets its power compared to the 78-79 versions. Which have a white wire instead of the blue one, maybe the white wire was cheaper The 74 version is an "animal" all to itself, I can only guess that is because it was the introduction year.
Here is a question for you......since you are apparently doing some testing on these things ....what is the brown wire, which isnt shown used on my diagrams, purpose for in life

Sparky

 

We seem to have a color conflict.:7 The module is a D5AE 12A199. It has red, white, and blue going to the three prong plug. If you hold the plug with the contacts towards you, blue is the odd contact. Holding the blue contact to your right so it is verticle, the top horizontal one goes to the red wire. The other goes to the white wire.

The other colors are black, green, purple, and orange. Purple and orange go to the magnetic pickup. Green to coil neg. Black is ground. This module has a flat gromet that is black in color.

 

I have a *NOTE in my Motorcraft book.

It says
All 1974 and early 75 original equipment modules contained a blue wire in the wire connector.Replacement modules do not require a blue wire.


Dennis

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Thanks Dennis, Does this mean that later modules only have two wires going to the 3 prong connector?

 

>We seem to have a color conflict.:7 The module is a D5AE
>12A199. It has red, white, and blue going to the three prong
>plug. If you hold the plug with the contacts towards you,
>blue is the odd contact. Holding the blue contact to your
>right so it is verticle, the top horizontal one goes to the
>red wire. The other goes to the white wire.
>
>The other colors are black, green, purple, and orange.
>Purple and orange go to the magnetic pickup. Green to coil
>neg. Black is ground. This module has a flat gromet that is
>black in color.

Wow that is just the way my diagram shows a 75....but totally different
Large connector
orange/yellow stripe = one side of dizzy pickup coil
black/green stripe = dizzy ground
pink/blue stripe = other side of dizzy pickup coil
green/yellow stripe = to coil negative terminal
Small connector
brown = not used
blue = 12 volts for run
red/blue stripe = 12 volts for start

I would tend to believe the motorcraft book.....I wonder why my diagrams are different????? They have always seem to work in the past. Of course they are aftermarket diagrams not the real Ford ones...but I have never noticed any problems until now

Sparky

 

The Notation is from the Motorcraft parts book.

After 1975 the wire colours change.


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[updated:LAST EDITED ON 03-Dec-02 AT 07:00 AM (EST)]I cleaned the ground surface on the distributor as well as the mounting surface of the ignition module. I then tested the red and white wires per Sparky's suggestion and the continuity of the green wire. Everything tested okay so I sprayed some starter fluid in the carburetor and it started. Thanks for everyone's help!

 

Did you check if the ga sis good and if your getting any gas at all??