Im helping my brother on his 79 f-100 ford 4x4 with a 1977 351m, now the engine cranks over but does not start, the duraspark module is new and so is the coil. If believe the problem is wiring, but not sure dont think its the silonoid or the starter since it does crank over, could you help me out thanks.

 

Do you have 12 volts on the coil with the keyswitch on? If you do, have you checked for spark? Take a plug wire off and put a screwdriver up in the end of the wire. While holding the plastic part of the screwdriver, hold the metal shank near the metal of the engine, and see if a spark jumps when you crank the motor.

 

I've put a test light on the terminals and the light is very dim, we had checked the spark from the main spark plug wire conected to the coil and did not see any spark

 

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Hi guys! tye, my 78 F150 351M 4x4 is acting the same way your bother's truck is. I know mine is in the ignition somewhere for sure. I replaced my ignition module when it first started doing this {this time} and it worked fine for a day then no fire again. I bought a new stator when I bought the module so I put that in and still no fire. I've been reading the old posts on the subject and some of the guys suggested a jumper wire from the batt.+ to the coil+ as a test. I did that and mine will start and run. but now I'm not sure where to go from there. I replaced the ignition switch, volt reg. and starter solenoid back in the summer when I had a similar problem. The ignition switch seam to fix it then but now it's back. I guess I'll put a new coil on it and check out the ignition switch again and look for shorts tomorrow. I'm wondering if maybe the ballast resistor could be causing the problem. Anyone out there know what it could be if it'll start and run with the jumper wire? Tye you could give the jumper wire a try and see if your brother's truck will start. Here's what Beartracks had to say about the jumper wire in one of his posts I was reading. "Try running a jumper wire from battery positive to the positive side of the coil and see if it will fire up. Don't keep running it this way if it works. Too much voltage for continuous running." I did a search on 'stator' in the electrical and 73 to 79 forums and found a lot of good info I could use. I just can't seem find the post I need yet. I'm sure it's there somewhere. Let me know what you find and I'll do the same. Good luck!
Ken,

 

If the truck only runs with the jumper wire to the coil....you are missing the voltage from the igntion switch.
There is a red/green striped wire from the igniton switch to the coil + ,which has a built in resistance to lower the 12 volts down to 9 or so.
There is also a red/green wire that goes to the starter relay "I" terminal, actually it turns into a brown wire on the way to the relay for reasons known only to Ford This gives 12 volts to the coil during starting........therory is it gives stronger spark for better starts.
So coming from the coil + is a red/green wire.........then comes a splice.........one wire from the splice is a brown one which goes to the starter relay "I" terminal.....another wire from the splice is a red/green wire (resistance wire) that goes to the igntion switch.
Now one would think this splice would be under the hood in the engine compartment......but it is actually on the inside of the cab behind the dash.
The brown wire leaves the relay...... goes thru the passenger side fire wall.......and meets the splice approx behind the steering column.....the red/green resistnace wire leaves the ignition switch does a few turns thru the wire harness and meets the splice.....then a red/green wire leaves the splice and goes out the drivers side firewall and eventually goes to the coil +.
At least that is the stock routing of the wiring. Hope this helps in your diagnosis of the problem.

 

Thanks sparky!
Your post helps! I have a wiring diagram and I see just what your talking about now. I'm still not running thou the weather has slowed me down. Is there a way to check the ignition switch with a multimeter when it's out of the truck? I wonder if Tye has had any luck. Thanks again Sparky!