Power wire to coil

[Corey Bowcutt]

When I get my engine back I am going back to a stock points/condenser distributor.  What came on the car when I bought it was an electronic ignition (not pertronix though).  Before I removed the engine from my car I measured the voltage coming from the firewall.  It measured 12 volts before going into a large resistor mounted at one of the valve cover screw locations.  A wire from the other side of the resistor went to the coil.  From what I understand the voltage going to the coil should be 6 volts?  I really do not want to use this kludgy resistor anymore.  I was looking at the wiring diagram and I see what looks like a resistor.  I assume this is what takes the 12 volts to 6 volts in the stock arrangement?  My question is what does this resistor really look like under the dash and where would I find it under there?  I would like to see if it was bypassed somehow.

Thank you,  Corey

[S7MS427]

Corey,

I think you'll find that what you have circled in your diagram is the resistor wire (should be a pink colored wire) that is part of the under dash harness.  There is no separate resistor.  With out seeing pictures of the harness in that area, it would be difficult to predict how much work would be involved to bring it back to stock.  One end of that wire should also be plugging into one of the tach leads.  Hope this helps.

[Royce Peterson]

Often an additional resistor is added when using the Mallory Unilite conversion or distributor. They are quite fragile and are more reliable when another Chrysler style resistor is added inline. They work with voltage as low as 5 volts.

Measuring voltage with no load is often inaccurate. Resistors don't necessarily do their job when in a no load situation. Your built in resistance wire may still be there. Use your eyes and look at the under dash wiring to see what has or has not been done.

[Corey Bowcutt]

These are both very useful posts for me.  What was installed was a Mollory unit.  And I in fact did measure the voltage with no load.  I am not terribly good with electrical stuff.  I will recheck once I get my engine back and installed.  In the mean time I will do a visual check under the dash.

Thank you both.

Corey

[S7MS427]

Corey,

It might help to pull the instrument cluster to have more access and prevent wear and tear on your back.

[Bob Gaines]

Chances are you will have a hard time seeing the pink resistance wire under the dash because it is typically wrapped up inside the wiring harness with the other wires.Typically the reason why a ballast resister is added under the hood is because the the built in resister wire has failed in some way.  It has shorted out etc. In this scenario a replacement wire with 12 volts is used to power the coil and the ballast resister is added to reduce the voltage under load.. The stock coil can not take 12 volts for a extended period of time  and will over heat and fail. Many after market coils will work with a straight 12V. Replacing the resister wire and putting it back inside the harness is very labor intensive. Replacing the underdash harness is typically less expensive if you are having someone do the work for you. Before I did that and after you have confirmed that the built in resister wire has failed and or replaced with a 12 volt all of the time connection I would install the ballast resister on the underdash side instead of under the hood . It will be out of sight out of mind. That will take some ingenuity but takes less time to install then installing a new underdash harness . Of course the savings of not having to buy a different underdash harness (new repro or good original) is a plus also . Just some information and alternatives to consider. 

[mygt350]

Bob, I was under impression pink resister wire was used to drop voltage so that the points and coil lived bit longer. Am I wrong?
Martin

[Bob Gaines]

Bob, I was under impression pink resister wire was used to drop voltage so that the points and coil lived bit longer. Am I wrong?
Martin

What I know is that the volt drop has to do with the coil .  The Ford coil does not have a internal resister. Many after market coils have a resister built in. If you run 12 volts to a yellow top coil for a extended time 20 ,30 minutes + the coil will get so hot you can't touch it. Back in my younger days we would sometimes bypass the ignition switch and resister wire direct from the battery to get power to start and run the car when no keys were available  . It is called hot wiring . I have seen some Ford coils that can't take the over heating and the after effects are the coils fail or they can explode under the hood . I recently surveyed the damage on a restored car under the hood caused by a exploding coil. It was pretty catastrophic for the restored 70 Mustang.

[gt350bp]

When I put my car together, I had missed plugging in the pink wire. When you would turn the key to start, the car would start, however as soon as you released the key it would stop. If I remember correctly, the pink wire was towards the middle of the dash and I knocked it loose when I mounted an on / off switch and indicator light for the electric fuel pump in the ash tray location.

Don
gt350bp

[mygt350]

When key is moved to start position, full 12 volts goes to coil and engine starts. When key is moved to the run position, the pink wire comes into the picture and drops voltage to 6 maybe 9 volts. So, if pink wire not connected, engine would die when you release the key to the run position.