66 f250
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Freshman User
Joined: Sep 2014
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From: Rice Lake WI
66 f250
So I just started to drive my 66 f250 but I have a problem. When the ignition is on with the heater on also, the wire from the ignition to the coil gets very hot and nearly burns other wires around it. I cant drive my truck without heat, any help would be appreciated. Thanks
Ford Parts Specialist
Joined: Nov 2006
Posts: 88,826
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From: Simi Valley, CA
COLF-12250-A .. Resistor Wire-Ignition Coil (Motorcraft DY-37) / Obsolete ~ Available NOS & from auto parts stores.
61.49" long / Color coded pink / 1.30-1.40 ohms resistance / #20 gauge wire.
Applications: ALL 1960/70 FoMoCo vehicles.
NOS =
GREEN SALES CO. in Cincinnati OH has 3 = 800-543-4959.
MCDONALD OBSOLETE PARTS CO. in Rockport IN has 3 = 812-359-4965.
WESLEY OBSOLETE PARTS in Liberty KY has 5 = 606-787-5293.
CARPENTER NOS OBSOLETE PARTS in Concord NC has 24 = 800-476=9653.
OBSOLETE RELIABLE PARTS in Nashville GA has 30 = 229-686-5101.
61.49" long / Color coded pink / 1.30-1.40 ohms resistance / #20 gauge wire.
Applications: ALL 1960/70 FoMoCo vehicles.
NOS =
GREEN SALES CO. in Cincinnati OH has 3 = 800-543-4959.
MCDONALD OBSOLETE PARTS CO. in Rockport IN has 3 = 812-359-4965.
WESLEY OBSOLETE PARTS in Liberty KY has 5 = 606-787-5293.
CARPENTER NOS OBSOLETE PARTS in Concord NC has 24 = 800-476=9653.
OBSOLETE RELIABLE PARTS in Nashville GA has 30 = 229-686-5101.
Postmaster
Joined: Apr 2002
Posts: 3,613
Likes: 6
From: Coal country
The coil wire starts out Red-Green from the switch, but then changes at the connector to Pink. This is a resistor wire, designed to lower the truck's system 12V down to about 5V or 6V. It can get uncomfortably hot as it is a resistor wire, but not enough to burn you or other wires. It is possible it has developed too much resistance, causing excessive heat. I have never seen one go bad, but it isn't impossible.
I would suspect then that there is a problem in the connections somewhere, such as corrosion or a poor ground. There are several connectors involved, so I would check them, especially the ones that can be exposed to the elements under the hood.
As for the heater, the wiring is not related to the coil circuits. Neither the coil wire nor the heater wire are connected to the same post on the backside of the ignition switch. The heater wire is Black/Green and is connected to the center post on the backside of the ignition switch.
EDIT: The wire that feeds the heater circuit is Black/Green, but only to the fuse box. It also feeds other circuits like the instrument panel. The wire that feeds the heater from the fusebox is Orange.
I would look there first to ensure the nut and the wiring connections there are tight.
In other words, the only shared current flow is power provided through the ignition switch.
The Yellow wire provides full-time power from the battery/alternator, to the ignition switch, even when the truck is off.
The center post on the switch has two wires. The Black/Green wire feeds the heater fuse and the radio fuse. (Note that the radio fuse also feeds some other functions, including the emergency flashers.)
The other wire on the center post, a Green/Red wire, provides switched power to the center post from the electrical system under the hood.
In short, I would suspect corrosion in the various connectors, poor grounds at the heater or the coil, loose connections (especially at the switch) or worn or burned contacts inside the ignition switch. It could even be a poor ground between the engine and the body.
I hope this has not been too confusing, and has helped at least a little.
I would suspect then that there is a problem in the connections somewhere, such as corrosion or a poor ground. There are several connectors involved, so I would check them, especially the ones that can be exposed to the elements under the hood.
As for the heater, the wiring is not related to the coil circuits. Neither the coil wire nor the heater wire are connected to the same post on the backside of the ignition switch. The heater wire is Black/Green and is connected to the center post on the backside of the ignition switch.
EDIT: The wire that feeds the heater circuit is Black/Green, but only to the fuse box. It also feeds other circuits like the instrument panel. The wire that feeds the heater from the fusebox is Orange.
I would look there first to ensure the nut and the wiring connections there are tight.
In other words, the only shared current flow is power provided through the ignition switch.
The Yellow wire provides full-time power from the battery/alternator, to the ignition switch, even when the truck is off.
The center post on the switch has two wires. The Black/Green wire feeds the heater fuse and the radio fuse. (Note that the radio fuse also feeds some other functions, including the emergency flashers.)
The other wire on the center post, a Green/Red wire, provides switched power to the center post from the electrical system under the hood.
In short, I would suspect corrosion in the various connectors, poor grounds at the heater or the coil, loose connections (especially at the switch) or worn or burned contacts inside the ignition switch. It could even be a poor ground between the engine and the body.
I hope this has not been too confusing, and has helped at least a little.
Thread Starter
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Freshman User
Joined: Sep 2014
Posts: 45
Likes: 0
From: Rice Lake WI
The coil wire starts out Red-Green from the switch, but then changes at the connector to Pink. This is a resistor wire, designed to lower the truck's system 12V down to about 5V or 6V. It can get uncomfortably hot as it is a resistor wire, but not enough to burn you or other wires. It is possible it has developed too much resistance, causing excessive heat. I have never seen one go bad, but it isn't impossible.
I would suspect then that there is a problem in the connections somewhere, such as corrosion or a poor ground. There are several connectors involved, so I would check them, especially the ones that can be exposed to the elements under the hood.
As for the heater, the wiring is not related to the coil circuits. Neither the coil wire nor the heater wire are connected to the same post. The heater wire is Black/Green and is connected to the center post on the backside of the ignition switch. I would look there first to ensure the nut and the wiring connections there are tight.
In other words, the only shared current flow is power provided through the ignition switch.
The Yellow wire provides full-time power from the battery/alternator, to the ignition switch, even when the truck is off.
The center post on the switch has two wires. The Black/Green wire feeds the heater fuse and the radio fuse. (Note that the radio fuse also feeds some other functions, including the emergency flashers.)
The other wire on the center post, a Green/Red wire, provides switched power to the center post from the electrical system under the hood.
In short, I would suspect corrosion in the various connectors, poor grounds at the heater or the coil, loose connections (especially at the switch) or worn or burned contacts inside the ignition switch. It could even be a poor ground between the engine and the body.
I hope this has not been too confusing, and has helped at least a little.
I would suspect then that there is a problem in the connections somewhere, such as corrosion or a poor ground. There are several connectors involved, so I would check them, especially the ones that can be exposed to the elements under the hood.
As for the heater, the wiring is not related to the coil circuits. Neither the coil wire nor the heater wire are connected to the same post. The heater wire is Black/Green and is connected to the center post on the backside of the ignition switch. I would look there first to ensure the nut and the wiring connections there are tight.
In other words, the only shared current flow is power provided through the ignition switch.
The Yellow wire provides full-time power from the battery/alternator, to the ignition switch, even when the truck is off.
The center post on the switch has two wires. The Black/Green wire feeds the heater fuse and the radio fuse. (Note that the radio fuse also feeds some other functions, including the emergency flashers.)
The other wire on the center post, a Green/Red wire, provides switched power to the center post from the electrical system under the hood.
In short, I would suspect corrosion in the various connectors, poor grounds at the heater or the coil, loose connections (especially at the switch) or worn or burned contacts inside the ignition switch. It could even be a poor ground between the engine and the body.
I hope this has not been too confusing, and has helped at least a little.
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