Ignition Resistor Wire... Where is It?
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Postmaster
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Ignition Resistor Wire... Where is It?
I am doing some preventative maintenance on my '78/F250 4 WD/400 equipped dent and cannot physically find the ignition resistor wire. My harness is unmolested.
The schematic in the FSM shows it between the switch and coil. I have un-taped the engine compartment harness. No resistor wire to be found there. Just a straight plain red wire running from the connectors near the drivers side firewall to coil +.
Where can I find it?
The schematic in the FSM shows it between the switch and coil. I have un-taped the engine compartment harness. No resistor wire to be found there. Just a straight plain red wire running from the connectors near the drivers side firewall to coil +.
Where can I find it?
Postmaster
Joined: Mar 2011
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From: Taxachusetts
From the ignition switch: Follow the red w/green trace..it should lead you to a splice. The resistor wire should say "resistor wire do not cut or splice," 4' 1" long, 1.30 - 1.40 ohms resistance, 16 gauge wire. It may be pink/red. I think it leads to a brown wire to the 'I' terminal on the solenoid.
D7AZ-12250-A, Motorcraft DY 213. ('73 and later) Another possibility - D7AZ-12250-A, Motorcraft DY - 84 -A, 60" long, red w/green stripe, 1.30 - 1.40 ohms, 16 gauge. Thanks to NumberDummy.
I may be wrong on the Motorcraft numbers....someone with more knowledge than me might be along.
D7AZ-12250-A, Motorcraft DY 213. ('73 and later) Another possibility - D7AZ-12250-A, Motorcraft DY - 84 -A, 60" long, red w/green stripe, 1.30 - 1.40 ohms, 16 gauge. Thanks to NumberDummy.
I may be wrong on the Motorcraft numbers....someone with more knowledge than me might be along.
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
Look at your firewall, towards the center, behind the engine. There should be a square, gray colored plug that has three wires going to it. One of these wires should be red w/ green trace. That should go back to the ignition switch. According to the Ford wiring schematic this is the resistor wire. It should have "resistor wire-do not cut or splice" printed on the insulation.
This is a picture of an earlier model ('73) that used a pink resistor wire.
This is a picture of an earlier model ('73) that used a pink resistor wire.
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
Filthy Beast, you're missing a digit in the Ford part numbers, the resistor wire is basic p/n 12250, the basic p/n 1225 is for wheel bearings.
'77-up models used the D7AZ-12250-A Motorcraft DY-213 resistor wire.
'77-up models used the D7AZ-12250-A Motorcraft DY-213 resistor wire.
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Postmaster
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Thanks guys. It sounds like it is in the cab in some cases (filthybeast) or in the engine compartment (Mike, 1973) in other cases.
I have opened up the engine harness and don't see it so I'll trace from the ignition switch.
I do have a replacement if needed and it is indeed around 4-5 feet long.
I have opened up the engine harness and don't see it so I'll trace from the ignition switch.
I do have a replacement if needed and it is indeed around 4-5 feet long.
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
From the ignition switch: Follow the red w/green trace..it should lead you to a splice. The resistor wire should say "resistor wire do not cut or splice," 4' 1" long, 1.30 - 1.40 ohms resistance, 16 gauge wire.
D7AZ-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-213) / Obsolete ~ Available NOS & from auto parts stores.
49" long / Color coded red with green stripes / 1.30-1.40 ohms resistance / #16 gauge wire.
Applications: 1977/89 F100/350, Bronco & Econoline.
D7AZ-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-213) / Obsolete ~ Available NOS & from auto parts stores.
49" long / Color coded red with green stripes / 1.30-1.40 ohms resistance / #16 gauge wire.
Applications: 1977/89 F100/350, Bronco & Econoline.
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Hotshot
Joined: Apr 2009
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From: Stanley, VA
The picture I posted is part of the under dash section of the resistor wire.
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Postmaster
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I found it (I think). Mostly wrapped up in original factory tape. Also routed with other wires from the switch up over the column to the firewall high on the drivers side where wires pass through to the engine compartment on my truck.
This service is mostly preventative after a flat bed ride home from a bad ignition switch. This resistor wire has been well protected and I guess it is pretty reliable to start with. At this point I see little benefit in disturbing it.
The new one with some alligator clips will go behind the seat just in case. In an emergency, I can jump the coil from the starter solenoid if need be.
I'll clean up the engine harness, make preventative replacement of the 40 YO original coil and coil connector, re-tape it and button it up.
This service is mostly preventative after a flat bed ride home from a bad ignition switch. This resistor wire has been well protected and I guess it is pretty reliable to start with. At this point I see little benefit in disturbing it.
The new one with some alligator clips will go behind the seat just in case. In an emergency, I can jump the coil from the starter solenoid if need be.
I'll clean up the engine harness, make preventative replacement of the 40 YO original coil and coil connector, re-tape it and button it up.
Postmaster
Joined: Mar 2011
Posts: 2,698
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From: Taxachusetts
You can test the resistor wire (for grins & chuckles) to see if it's history:
Key in "RUN," engine off, the DVOM + to coil + and the negative to a good ground.
If you read between 6 - 8 VDC, the wire is good. Any more or less voltage, the resistor wire is shot. You probably knew that already.......
@ NumberDummy - Thanks for the correction...I'm off today! Must be too much blood in my alcohol system
Key in "RUN," engine off, the DVOM + to coil + and the negative to a good ground.
If you read between 6 - 8 VDC, the wire is good. Any more or less voltage, the resistor wire is shot. You probably knew that already.......
@ NumberDummy - Thanks for the correction...I'm off today! Must be too much blood in my alcohol system
Postmaster
Joined: Mar 2011
Posts: 2,698
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From: Taxachusetts
If no resistance wire is used, the coil would overheat and go bad.
HEI equipped vehicles don't use a resistance wire - they need a constant 12 volts DC.
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Postmaster
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As an update, its back together and voltage checks good. Also running sweet with fresh tuneup. My new resistor wire is rigged with alligator clamps and behind the seat just in case. Thanks for the assist.