Wire Getting Hot!!

351w carbd, c6 trans, no EEC.  So ive just found out a power wire (14 gauge red/green stripe) is getting hot.  The wire is located in the engine bay, in a loom that ran along the drivers side up to the front of the engine bay.  This wire was connected to a thick brown/pink strip wire, and a smaller 16 gauge red/green stripe wire.  It seems the small red/green stripe wire provides power to the ignition components (duraspark, coil, etc.), i dont know what the brown/pink stripe wire is for, the 14 gauge red/green stripe wire is 12v in on position.  when all three are connected, the 14 gauge red/green stripe wire gets hot, and volts read at 6v.  when the smaller 16 gauge red/green strip wire is disconnected from the brown/pink + 14 gauge red/green stripe, the wire doesnt get hot, and the voltage reads at 12v.  Obivously the problem lies in the smaller 16 gauge red/green stripe wire, but i cannot find out where!!!  the smaller 16 gauge red/green stripe isnt a power wire, it receives it from the thicker 14 gauge red/green stripe wire.  Unfortunately the smaller 16 gauge red/green stripe wire in needed to start the engine.  Any help would be appreciated!!

Attached is a diagram that should help you diagnose the problem.  There is a radio noise capacitor hanging off that wire, try disconnecting the capacitor, it may be shorted.

Good luck,

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Seabronc said:

Attached is a diagram that should help you diagnose the problem.  There is a radio noise capacitor hanging off that wire, try disconnecting the capacitor, it may be shorted.

Good luck,

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Click to expand...

The diagram looks like it applies to EEC equipped rigs.  My B-Co does not have the EEC. Also, from inspecting the wiring, i dont see a radio noise capacitor..any other suggestions??

Unfortunately I don't have the non eec diagram, but the diagram should be close enough for the wires you are talking about.  It does hook to the coil so you need to disconnect the coil and see if it still gets hot with the key on. If it still gets hot, you need to locate the short among the remaining connections.  It won't be a direct short or it would blow a fuse, it most likely is a high resistance short.

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I was pretty tired last night when I responded.  

Does the engine run when everything is connected?

How are you disconnecting it? (connector or cutting the wire).  

One of those wires is a ballast wire, (the Ford equivalent of a ballast resistor). My thought is that the one which is heating up is the ballast wire and would not heat up if the coil is not hooked up.  It is a resister that reduces the voltage to the coil.

Here is a Duraspark II diagram.  It is probably closer to what you have with the exception of color codes.  I'll keep looking for one that matches yours.

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Seabronc said:

I was pretty tired last night when I responded.  

Does the engine run when everything is connected?

How are you disconnecting it? (connector or cutting the wire).  

One of those wires is a ballast wire, (the Ford equivalent of a ballast resistor). My thought is that the one which is heating up is the ballast wire and would not heat up if the coil is not hooked up.  It is a resister that reduces the voltage to the coil.

Here is a Duraspark II diagram.  It is probably closer to what you have with the exception of color codes.  I'll keep looking for one that matches yours.

Click to expand...

The engine runs fine-ish with everything connected as it was.  I have some air/fuel mixture issues to work out, so i dont think the electrical problem has to do with that.  Nonetheless, the engine turns over and cranks up fine with everything connected.  The problem is, the 14 gauge red/green strip wire gets hot when all three are connected (16 gauge red/green stripe + 14 gauge red/green stripe + brown/pink stripe.  If either of these wires are disconnected, the B-Co will not start.  I dont think that the 14 gauge red/green stripe wire is the ballast wire, because when it is disconnected and tested by itself, it has 12v keyed power.  However, when all three are connected and tested, the voltage is around 6v.  The previously mentioned three wires were mated together from the factory.  I just cut that connection for the sake of quick connect and disconnect while testing.  I should also mention, that no other wire heats up except the 14 gauge red/green stripe.  Even when it is connected to everything, it is the only one.  I actually ordered the ballast resistor when i installed the MSD coil a while back, just as a precaution.  My guess is, this ballast resistor is necessary if the ballast wire is not present.  My engine bay caught fire several years back and i rewired alot.  Maybe the ballast wire got burned up in that fiasco.  I will try the ballast resistor to see if that works, but how do i wire it in?  do i connect the keyed 12v 14 gauge red/green strip wire to one side, and the brown/pink strip and 16 gauge red/green stripe to the other side??  Thanks for all your help!!

Yo B,

Suggest Calling MSD Tech Line:

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see ph #

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Incl all info incl what you wrote here; my one Q is; do you have the MSD 6A

No, it still has the duraspark ignition, I only replaced the coil with MSD coil.

The function of the ballast is to reduce the voltage to the coil.  The result you are getting is exactly what I would expect from the a ballast wire.  With no connection to the coil I would expect 12V at that point, when hooked up I would expect to see the voltage drop at that point.  If you look at the diagram, with the key in the start position the coil gets direct 12V but as the key is turned to the RUN position the ballast is introduced to reduce the voltage at the coil.  If the coil had 12V all the time it would overheat and fry.  That is the design of the system.  

So what I'm telling you is that there is nothing wrong.  Hopefully this diagram will make it easier for you to visualize. The point you are looking at is between the ballast and the coil.  When the key is in the S position the coil primary gets direct 12V for starting. When the key is in the R position the 12V is applied through the ballast wire/resistor.  Current flow through the primary and ballast causes 1/2 to be dropped across the ballast and 1/2 to be dropped across the primary, it's simple ohms law.  If the resistance across each of the two components is equal each will show 6V across it, total of 12V.  When you disconnect the wires there is no current flow through the system so there will be no voltage drop across the ballast wire/resistor resulting in an indicated 12V at that point.

If you add that ballast resistor to the circuit you will reduce the voltage to the primary to 1/3 of the total 12V and only have about 4V at the primary which will make your spark weaker.

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I can recognize all of the components in the diagram, I'm just not very good with applying electrical diagrams. So should I just ignore the keyed 12v wire heating up??

Okay, so im getting severly screwed up the more i dig into this problem.  Trying to find out why the wire is heating up, I now found that I am getting around 6v at the positive side of the coil with the key on, AND, im getting around 1.3v at the tach side!!  How is that possible??  With the engine running, I get around 9v at the positive side and 6v at the tach side.  Maybe all of these electrical problems are related but i dont know how or where to start solving this thing!! Please help!!!!

They are not problems, it is just how it works.  Yes those results are possible.  The 1.3V at the tac side represents the voltage drop across the components in the control module. With the key on and engine  not running you will get the static result of 6V at the coil.  With the engine running you will have an inductance induced voltage caused by the expanding and collapsing of the electrical field around the primary and secondary.

Yes, it is normal for a resistance wire or ballast resistor to heat up.

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