Ignition problem
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Freshman User
Joined: Oct 2008
Posts: 35
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From: Eugene, Or
Ignition problem
So, I have a 72' with a 6cly and a manual transmission. I seem to be burning coils up on a regular basis so I did some checking and it appears that I have a full 12v feeding to the coil when in the "RUN" position on the ignition switch. What could be causing this? I have also noted that when I go to the "START" position that the voltage from the solenoid feeding the 12v for hot start drops to 8v... Is it possible that the resistance wire has somehow fried causing a 12v constant to the coil? All wiring appears to be stock and in the factory harnessing. I am a little confused by all of this and any help in the right direction is appreciated.
Senior User
Joined: Dec 2002
Posts: 473
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From: SW Florida
Well it should definitely only be getting about 6V when it's running and should only have 12V when the key is in the start position.
There is a resistor built into the hardness as you surmise, and there is a second feed wire that comes off the starter solenoid that provides the 12V when the ignition is engaged to help the truck start. There are 2 small terminals on the solenoid, one engages the starter when it receives 12V from the starter switch and the other is the one that goes to the coil.
Is it possible somebody hacked into the harness and removed the resistor? I don't know how anything could have burned up and caused the resistor to start providing 12V... Seems like it had to be removed or bypassed.
There is a resistor built into the hardness as you surmise, and there is a second feed wire that comes off the starter solenoid that provides the 12V when the ignition is engaged to help the truck start. There are 2 small terminals on the solenoid, one engages the starter when it receives 12V from the starter switch and the other is the one that goes to the coil.
Is it possible somebody hacked into the harness and removed the resistor? I don't know how anything could have burned up and caused the resistor to start providing 12V... Seems like it had to be removed or bypassed.
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Freshman User
Joined: Oct 2008
Posts: 35
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From: Eugene, Or
Well I figured out one of the problems. I couldn't see why there was a voltage drop at the solenoid till I did some more thinking... or maybe less thinking... During our initial research I 12v seemed to be everywhere in the system. Then I did a quick reading from the battery to the solenoid and found that there was a 4v drop... Cleaned the terminals up and wham bam thank you ma'am all 12v at the solenoid. Reached into the window and the truck fired right up.
As for the resistor, I was under the impression that the wire itself was what caused the resistance. I know the full 12v comes from the solenoid when you turn to the start position. Not sure why it stays at 12v... I had some theory but forgot what I was thinking last night.
I do have an electronic ignition to install at some point but wasn't gonna go that route until after I built my 300 to put in it. DUII or whatever the stock Ford electronic ignition is.
As for the resistor, I was under the impression that the wire itself was what caused the resistance. I know the full 12v comes from the solenoid when you turn to the start position. Not sure why it stays at 12v... I had some theory but forgot what I was thinking last night.
I do have an electronic ignition to install at some point but wasn't gonna go that route until after I built my 300 to put in it. DUII or whatever the stock Ford electronic ignition is.
