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Old 06-29-2011, 01:55 PM
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puroford puroford is offline
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Ignition Coil Wiring

Hello,

I bought a 79 F100 with a 460 swap. An older points distributor was used (do not know what year). It is wired in and the trucks starts and drives. I want to know how to correctly wire it so that it turns on from the key not a switch. Currently it is wired in as follows:

The black wire from the distributor is wired to the coil. Then the positive side of the coil is wired straight to the battery with a switch. So to turn on the truck, I have to hit the switch to the on position and then go turn the key. To turn it off, i have to hit the switch to the off position. So the key is not the ignition source at this time.

1) Does it affect the coil to run directly off the battery?
2) How can i wire it to run off the ignition key?

Any help is appreciated. Thank you
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Old 06-29-2011, 03:02 PM
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The factory ignition system (whether points, or year-correct electronic ignition) powers the ignition coil through a ballast resistor with the key in RUN. When the key is turned to START, the ballast resistor is bypassed, and the battery is directly connected to the coil, since the battery voltage drops while the starter turns over. With that in mind:

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Originally Posted by puroford View Post
1) Does it affect the coil to run directly off the battery?
Yes, if this is the factory coil for use with an external ballast, then running the full battery voltage will overheat the coil.

Quote:
Originally Posted by puroford View Post
2) How can i wire it to run off the ignition key?
Ignition switches have at least one post that is hot-in-START only. This typically powers the starter solenoid. The coil must be fed hot-in-START power as well. If the ignition switch has a second hot-in-START terminal, the coil can be powered from this in START mode. If not, the starter solenoid typically has an 'I' terminal that is hot-in-START. In this case, the starter solenoid actually powers the ignition coil in START. This is referred to as the start bypass circuit for the coil.

The ignition switch should have a separate terminal that is hot-in-RUN to power the coil. In RUN, the coil should be powered through the ballast. In the factory setup, the ballast is actually a length of specially-doped resistor wire. It should be pink, or red, and marked with "RESISTOR WIRE - DO NOT SPLICE." If this is long gone, you can typically find generic ballast resistors at most parts stores. You should use 1.3 to 1.4 ohm in this case.

I don't have a spare factory switch around, so I can't help much with what terminals of the switch do what - but this could be done very easily yourself with a continuity check.
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Old 06-30-2011, 02:03 PM
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puroford puroford is offline
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Thank you for your quick reply.
So.........
If i find the pink wire marked resistor, can i wire it just to that? The wiring is still there, it is attached to a black cap that went onto the coil. There is a green/red wire and i believe the other is the pink one. Should i be fine jsut wiring it to that one?

Or

Can i run it to the "I" post with a resistor in the middle? Will this activate the coil with the key?

I will try to get pictures up.

Thank you for your help/
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Old 07-04-2011, 09:58 AM
JoeHarbourJets JoeHarbourJets is offline
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You should be able to buy a generic ignition switch. I installed one on my truck a while back. It has 4 poles. I can confirm later when I get a chance to look at it, but I'm pretty sure the pink resistor wire goes to an R (or sometimes marked "I") pole of the ignition switch. That wire splits into 2 wires one the engine side of the firewall. On my system, one of these is a red/green wire that goes to the coil. The other is a brown wire that goes to the I pole of the solenoid switch. There is also a red/blue wire that goes from the S pole of the ignition switch to the S pole of the solenoid Switch. Anyway, I don't want to get further into it until I check my system later. I'll get back to you then.
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Old 07-05-2011, 09:04 AM
JoeHarbourJets JoeHarbourJets is offline
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Rather than trying to explain it, try this thread and diagram:

http://www.ford-trucks.com/forums/10...positions.html
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Old 07-05-2011, 09:04 AM
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