Hi Guys, I have a question for you guys and hope to find the answer here.

To give a little background:
I have a 1971 F250 Camper Special RWD with a 390,

Just so you guys know, It has a electric fuel pump that is under the cab where the gas lines are, mounted on the frame rail and grounded.
It has 2 brand new gas tanks, replaced fuel lines, and a Holley 4160 carb - (its not a gas issue).
I just switched out the stock coil for a edelbrock 12V , and petronix ignite. it's wired by a 12v lead thats jumped from the fuse box straight to the coil.

It's been very reliable until the other day when something weird happened.
When I went to fire up the truck it cranked but would instantly die after.
The starter was getting the spark. the battery is fully charged. there was spark to the plugs, coil, etc - but no matter how long i would crank for, it wouldn't fire up and run, apart from one random time and i managed to drive it home.

I adjusted the carb back to stock settings, and started to read about what this issue can be.

I replaced the petronix, just on the off chance it was that. I have a new rotor cap, and distributor cap. New spark plugs. Like I said the coil is brand new.
When I turn the key its still not catching straight away - it'll crank for a while and pretty much just when i let go of the key, sometimes it will fire up at that point.
While I was trying to understand this issue, i noticed the smell of smoke coming from the ignition switch.

I have a D0TZ-11572-A ignition switch. I did the Ohms test and it seemed to be fine.
out the back are 6 wires going into 5 ports. the port that has two wires connecting into one - has a slim wire and a fat one. the fat, light pink wire is getting super hot -
I have disconnected the battery, and scratchign my head as to how to resolve this.


Does anyone have an idea of what I need to do here? do I need to switch out the ignititon switch wiring harness, and if so know where I can source that, and diagrams if there are any?
I will stand by for some advice thanks to you all in advance!

Micoole

Here is the pic of the switch wires,

 

https://www.fordification.com/tech/schematics_h.htm.
Here are some wiring diagrams. It doesnt show one specific for 71 but Im sure it probably the same as the 72 for the most part. On my 72 f250, I bounce back and forth from the 70 and 72. The bigger pink wire is the resistor wire for the coil to the distributor. If that wiring is still hooked up, that ir probably a problem. I will be running an HEI on my 72 that needs 12V all the time, so I deleted the resistor wire from the ignition switch and replaced it with( I forget what gauge wire I used) a wire straight to the coil. If you ran a wire from your fuse box, wouldnt that have 12V running to the coil 24/7? Im not sure on that but its not a way I have seen anyone power the coil before. In the wiring diagram you will see with the original setup, when you turn key to start, you get 12V from the battery through the starter solenoid. When key is let off to run, the power was rerouted through the ignition switch and the resistor wire to the coil. The wire with the resistor wire goes to the starter solenoid. I would definitely change that. I dont know if that is your only problem though.

 

Before you just automatically change the starter solenoid/relay you can see if that’s the problem by simply disconnecting the small brown wire from the right side “I“ terminal.
That separates the starter system from the ignition system, except for the ignition switch itself.

If the problem goes away, you can replace the starter relay. If it persists after disconnecting the brown wire, then the fault is either in the ignition switch or some of the wiring.

I agree with 1browski about not using one of the fuses directly to the coil. There are both switched and unswitched fuses, so presumably use used a switched one. But the issue becomes, the fact that it’s hot in ACC as well as ON so you can’t just sit there listening to the radio anymore without overheating the ignition coil.

 

Oh, and while you are not supposed to smell smoke coming from the region of the ignition switch (obviously) the resistor wire does get hot under its normal operation.
They typically run it separately from the rest of the harness with a heat resistant jacket around it, so as not to damage the surrounding wires.
Is that how yours is run after you get a few inches from the ignition switch?

 

And I could never remember. When did Ford change from the early troublesome ignition switch to the later improved model?

 

During 1970. Difference is before and after serial number G90,001.

 

OP, I think the problem may have risen depending on what you did with the pink wire from switch to wiring junction coming from the "I" terminal on the starter solenoid. And how you sourced the 12V you ran from fuse box to coil. As stated above, I hope you picked a switched fuse. Below I will post a schematic of a 1970. Same same. You will note at the ignition switch the two wires yours have are circuit #932 and @16. Focus on @16. It is the pink resistor wire. Where you terminated that @16 wire should have 6 to 9 volts with the ignition switch "on". At the termination, something might have happened so now that wire is shorted to ground when powered. Note @16 wire went to a connector where #262 wire from the "I" terminal on the starter solenoid came from. Originally that is how the coil got 12V during "start'. This #262 wire still needs to be working as designed during "start". Check the "+" side of the coil to have 12V during start and on (run). But not with the switch "off". Also check if the coil you bought is meant to have an external resistor or not. Some do and some are meant for a full 12V. Either the box or the side of the coil should say.


If the problem isn't found after doing this, then change the switch. It is possible what happened to the @16 wire might have made the switch give up the ghost on the inside.