I have been having problems with the '79 Ford F100 not starting from time to time. I think I have finally backed into what I think is the problem. I seem to get no power to the module but the bat side of the coil will have power. Somewhere those two lines have a common feed and separate either at or near a ballast resistor. I sure could use a good wiring diagram to locate where all of these connections are. The manuals I bought (Helm) when the truck was new doesn't have one. I would like to know if any of the counter books like Haynes have a detailed diagram. It looks like I need to figure out why I have no power to the module and repair or bypass the wire. But I have to know from where to start.

Looking for help here!

Clark

 

You may want to check the grounds. I had a chorekee that had the same problem. It was traced to a ground wire that was to short and broke the wires internal of the insulation. You could not see the wires to know they were broken. But moving the wiring harness it would die. Just like some one was turning the key off going down the road.

 

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the connector at the distributor has caused problems in the past
wires will break inside it and cause an intermitant problem

 

As well as the connectors to the distributor.

Wires there also break off or fray

 

Here is the problem I have been having. Occasionally the truck will either not start or while driving the engine will stop and not restart. Under either no start condition it appears that there is no spark. I have substituted a new ignition module and it still would not start with no spark. I have substituted a new coil and still no spark. I have even replaced the pickup inside the distributor and no change. Since that is all of the ignition components, I have been checking connections. Everything seems to connect well with no frayed or broken wires. I worked on this last weekend and it started fine. I went out to drive it to work on Monday and it wouldn't start for nothing. Yesterday, it started up like a new one.

I'm confused about the two wire connector (red and white wire) to the ignition module. Everything I have read indicates that the red wire is hot with the ignition switch in the run position and the white wire is hot in the start position to allow a change in timing for starting. With the connector pulled apart, I get no voltage on the red wire but battery voltage on the white wire with the switch in the run position. My Ford manual indicates that you should test the red wire with the connector assembled. If you do that the red wire has voltage on it. So does the red wire come from the ignition switch or does the module provide a voltage to the red wire? If so where does it go from there?

I'm afraid that this is one of those hard to find wiring problems. While it was running yesterday I pulled, shook, moved all of the wiring and connectors to see if that caused a shutdown. I couldn't get it to stop.

Any words of encouragement?

 

Try running a jumper wire directly from the Battery + to wire the connector that plugs into the I terminal of the starter relay..then try and start the engine.
It that still doesn't work....place the jumper wire directly from the battery + to the + terminal of the coil

 

So Dennis, you are thinking that the coil may not be getting full voltage during start or no voltage at all? Defective connection in the starter relay?

 

Right now we are troubleshooting wiring.

Process of elimination

 

It has behaved properly today. I do have a set of test leads that I am carrying now that I can use to apply voltage directly to the coil. Now its a wait and see game. Thanks Dennis!

 

I clean all my ignition connections twice a year.

Aside from the battery terminals I clean any charging circuit connection once a year.

Even though we have a dry climate corrosion gets everywhere.