Gremlins: Constant 12V power to ignition wire?

1968 GT-E 427, I am getting it running again after four years in storage. I have just rebuilt the Holley List 4088 carb, amazing how old fuel turns into hard varnish! The ultrasonic cleaner was my friend for this job.

The problem I have is that the red wire/green stripe that come from the firewall to the positive side of the coil is getting constant 12V, even with ignition switch off and key removed. My understanding is that it should not get any volts when ignition is off, and when ignition switch is on it should be 6V via the pink wire resistor - right? Electrics stump me every time. I can stare at wiring diagrams all day or just ask the smart people on this forum!


You are correct; that line should be 0 volts except when the key is in RUN or CRANK.
In the meantime, it would be best to disconnect the battery when the car is not in use as this line could drain the battery and burn up the points (if you still use them).

Might be a bad reading on the meter. Use a 12 volt test lamp to see if the lamp lights. Should be more like 9 volts with the engine off, 11 volts at idle. That is if the battery is fully charged at 13 ish volts.

Another symptom - starter motor is not engaging to crank engine.

I am now thinking it is a starter solenoid problem. The only time there should be 12V power to the coil is on cranking, via the brown wire from memory. No crank and 12v power to the coil indicates the starter solenoid is the culprit. Not sure what is actually happening in there, but I will swap out the solenoid and see if that fixes it.

Better to use a meter and a 12 Volt test lamp then figure out the actual problem before throwing expensive parts at it.

See if there is power to the starter.

So there is constant 12v power from the ‘I’ post on the solenoid, even when key is not in the ignition.

The starter motor engages when a screwdriver is arced across the solenoid red terminal to the ‘S’ post.

Turning the ignition key doesn’t seem to do anything.

If it was an ignition switch problem it would probably be activating the entire solenoid right? Ie, engage the starter motor and 12V power on the ‘I’ post.

So I figure that somehow in my barely used Motorcraft D2A5 solenoid, there is now a permanent connection between the red terminal and the ‘I’ post, but is not touching the ‘S’ post.

Should be simple to test with a test lamp. I would not use a meter, a lamp will tell if there is real voltage present.

The I post is directly connected to the starter side of the solenoid. And that is connected to the starter which is a very low resistance connection, essentially a ground. So any hot wire connected to that would get very hot and you would see a lot of current on it that should blow what ever fuse might be involved or burn up the wire. Perhaps you have a second starter relay at the starter as found on some non stock starters.

Ok, resolved with a new starter solenoid (repro type). Now starting and running just fine.

The D2A5 Ford solenoid was definitely arcing a connection between the live terminal and the ‘I’ terminal. Don’t know what was going on inside the device.