Have '84 F-150 w/302-C6. Sometimes dies when hot, but will continue running if ignition switch placed in "Start" (as opposed to "Run") position. This has only recently become a funtioning issue, although gas milage has continually been poor dispite all remedies applied. I think the milage deteriorated after this cut off switch issue, but the running has never been an issue that I recall, until recently. Where and what circut allows engine to continue running in this position?(BTW: I have a push button starter I installed rather than an ign switch one, so I can place the ign switch in "Start" even when engine is running w/o starter engaging.) I remember old Chrysler's had ballast resistor and wiring to bypass the 'run' wiring when starting to provide more juice to ign circut during cranking. Over the years I have replaced and worked on all factors from ign module to distributor, coil and pickup, w/o changing these dynamics. I used to have an ign cut off switch to the ign module that became heated (wires) when running, which I deleted upon discovering the heated wiring (wire gauge too small for current I suppose.) There is a brain in this truck which has never been touched, can it cause intermittent run issues, and would it be affected by such too small wiring? What happens when Start position engaged that doesn't happen when ign in "Run"? Over the past 22 years this truck and I have been all over the country and it has paid for itself many times over. Thanks to all!

 

looks like there might be a resistance wire in this one too. hope this helps.

 

I would try replacing the ignition module. It's common failure mode is heat related.

 

There are several fusable links in this unit, all of which I think fry when overloaded like regular fuses. As for the ign module, it has been replaced well after the ign cutoff switch was replaced. I am not familiar with the brains of these units and am hoping someone knows more than me in that area. I have replaced and rebuilt every part and unit on this truck during the 22 years I've owned it, but have never been able to figure this glitch out. I am not a "replace till you find the culprit" wrench and can trouble shoot circuts and systems, I just don't know much about the circutry for ign bypass @ start position vs: run position, and which components are directly energized. The schematics I have via Motors, Chiltons, etc are not detailed enough, and leave that part out in the texts I have. Thanks! Bob-O

 

Go get a Haynes manual from the autoparts store. They have good factory diagrams on your model in the back of the book, and will show you everything you questioned in your post. The 84-86 diagrams are very good in this book.

 

According to wiring diagrams in back of Haynes Ford
Pick-Ups Bronco, 1980 thru 1991, Page 351.
Power comes from START terminal of ignition switch to wire splice to ignition coil. It is hard to read the wire color. I believe it is either OR-PK( orange-pink) or BR-PK (brown-Pink)

Power comes from RUN terminal of ignition switch thru 1.05-1.15 ohm resistor to the splice in the start circuit. The wire color is R-LG ( red-light green).

I believe your problem is either a bad ign switch, wiring or a resistor that opens up after it overheats.

Happy Hunting.

 

Thanks Franklin2, Payday33, I have several manuals (not Haynes...Yet and what I ran into was the diagram left off the ign switch. I wnated that particular circut to see what is bypassed and so to determine what could be bad. My diagrams show a wire "to ign switch." That's it, no more. If I can see where circut goes from ign switch 'run' and 'start' positions, then I can better determine what to do. Payday, I have never seen a resistor in a car circut, is that resistor wire? Thanks for responding!! I have a 96 Escort wagon that had a crazzy wiring issue resolved through this forum (was 'Sarge' who responded re: broken hatchback door wires and described my symptoms exactly. I then ripped out and replaced 21' of multiple fried wiring to fix I try to do my best to pass that experience on. Ciao, Bob-O

 

I would guess that resistor is actually a resistor wire. Ford has been using resistor wire for the coil power for many decades before the electronic ignition came along, I see no reason they would change resistor types.
I would place money on either a bad connection somewhere in that resistor wire, or a bad ignition switch being the underlying cause all along.

 

According to Haynes on page 166, "The ballast resistor is actually a specific length of special wire used to limit the primary ignition circuit in the run mode. It is part of the vehicle wiring harness inside the passenger compartment and under no circumstances should it be cut, spliced or replaced by any other type of non-resistance wire".

Hope you find it.

 

Thanks PayDay33! I will research this ballast item, although I never heard of it in Ford products (only Chrysler that I recall) but it is possible that I damaged it or it is just deteriorated. As it is, when the engine stalls it can be brought back to life by placing the ign key switch in the 'Start' position. I would like to know where the current goes in this position that it doesn't in the 'Run' position. I will try to locate the proper schematic, start new project Monday and am prepping for that. I need a 'round-tuit!'
Ciao, Bob-O

 

The Haynes schematics do break down the internal workings of the switch.

 

When you need a Dentist, you don't go to a Carpenter. That's what this forum is, and I appreciate all your responses. If the Haynes diagram shows the difference in the circuts path from the Start and Run positions, then I can drill out the bad, and fill it with the good Thanks! Ciao, Bob-O

 

From some schematics I saw here a while back, while in the start, its a direction 12v connection to the ignition coil, but in run, it uses the resistor wire to go to the coil.

 

Thanks Lead Head, I gotta get a copy! I thought there was supposed to be a 7.2v+_ run position voltage from one of the texts I researched while trying to diagnose this glitch, and that would be supported by the presence of the resistor wire in that circut. Things are beginniing to clear up for me with this issue thanks to all of you who have responded. Just like my 5yo sings "Bob the Builder...Working together to get the job done" Ciao, Bob-O

 

One of the issues is locating the resistor wire in that particular circut, and that may be interesting. I'll have to go to the Dealer to see if they have the actual manual for that year where they actually describe and picture where each component is located. Thanks again. Bob-O