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Ford resistor wire, $30 is about as cheap as you'll find. I did it on my 66 Fairlane. It was easier to replace for me than build a like scenerio. Yes you need it for your current configuration.
jetfixer thanks for the reply. I did see that one on NPD website but it says ford trucks up to 72, so I thought that meant it won’t work for me. I guess that means it is not plug and play? I’m ok with cutting the ends off and putting the connector I need as long as it drops the correct amount.
jetfixer thanks for the reply. I did see that one on NPD website but it says ford trucks up to 72, so I thought that meant it won’t work for me. I guess that means it is not plug and play? I’m ok with cutting the ends off and putting the connector I need as long as it drops the correct amount.
It is probably just different length or different ends on it. My coil was way down on voltage with the almost 60 year old wire. After replacing it, my voltage is 8.9 to 9.2 volts while running.
Ok … I’m at a loss. I used my multimeter to find the 80 ohm wire ends, at the engine side firewall plug and the ignition key. I CAREFULLY cut away the electrical tape on the harness behind the dash and traced the wire from the ignition key to the inside firewall. It’s a single wire all the way to the inside firewall, but the engine side firewall has TWO wires of matching color and stripe … WHERE IS THE RESISTOR WIRE?! 😤
Point A that has 80 ohms Point B that has 80 ohms The place for point B terminal Two wires coming from point B(ignition key). One goes to the driver side firewall and the other goes to the passenger side/glove box area.
Ok, I found the resistor wire under the dash. I tested the ohms on both ends of it, at the key and plug on engine side firewall, it is 1.3 ohms. I reconnected the plug and then tested ohms of resistor wire at key to positive coil and it was 1.3 ohms … is my resistor wire fine? I just tested ohms of resistor at key and engine side firewall plug while I moved the resistor wire around at every point along the wire. There was zero change in ohms, so I’m pretty sure it’s not broken and the ohm is good. I’m completely F’ing lost now. Why am I getting less then 4volts at the coil.
I test volts at coil with key on, almost 12volts. I started the truck and let it idle in the driveway. Reconfirmed +\-4 volts at coil while running. When I increased rpm’s the volts dropped to low 3’s high 2’s. After idling for awhile it cut out. I quickly pulled the plugs apart and retested the resistor wire at key and engine side firewall, zero ohms. I guess that makes sense because the voltage dropped is lost as heat? I measured ohms at the red wire on the ICM and resistor wire at key(previously measured at 80ish ohm) it was just under 80 BUT THEN I heard my electric cooling fan turn on and the ohms dropped into the 60’s … when the fan turned off the ohms went back to 80 … WHAT THE ACTUAL F MAN! Do I have a bad ground somewhere? Once all this gets figured out I’m buying a round for all the people that helped!
It could be a ground, because the resistor wire is testing within spec according to your last post.
There should be a ground on back of head to firewall, might clean the contact area and terminals on both ends and do the same for the battery negative cable, which on mine bolts to the engine block below the alternator. Make sure your alternator has good contact too where it bolts to the engine.
The constantly jumping voltage makes me wonder if there is a possible issue with the voltage regulator, but I would start with cleaning all the grounds in the engine bay first. Wouldn't be a bad idea to add an engine to frame ground too if you do not have one already.
The other option could be the ignition switch itself and might be a loose or corroded contact inside which is causing the intermittent issues.
This is why many hate working on the electrical system. There are so many variables and possible causes and it makes it even more difficult when the issue is intermittent.
Just to clarify, I followed the coil positive wire to a plug on the firewall. I checked ohm between those two points, 0.1 ohm. I followed the other side of that plug to the ignition switch(which was the resistor wire). I tested ohms from coil positive to ignition switch and got 1.8, I know that’s higher than the recommended of 1.05-1.15 but is it still within range? The new resistor wire I have tested at 1.3 ohms, so maybe it’s my meter 🤷🏼♂️ when I test from the red wire on ICM to the coil positive I get 80 ohms. But that’s not one wire, that route goes through the ignition switch or ICM right?
Just to clarify, I followed the coil positive wire to a plug on the firewall. I checked ohm between those two points, 0.1 ohm. I followed the other side of that plug to the ignition switch(which was the resistor wire). I tested ohms from coil positive to ignition switch and got 1.8, I know that’s higher than the recommended of 1.05-1.15 but is it still within range? The new resistor wire I have tested at 1.3 ohms, so maybe it’s my meter 🤷🏼♂️ when I test from the red wire on ICM to the coil positive I get 80 ohms. But that’s not one wire, that route goes through the ignition switch or ICM right?
The wire from ICM to coil does route through ignition switch per the wiring schematics I have looked at. That additional resistance could indicate an issue with the ignition switch itself. You could use a short length of wire to make a jumper across the terminals that plug into the back of the switch to complete the circuit without the switch and test the circuit again. If you are near 1.3 ohms again, that would be a good indication that the switch is causing issues.
The wire from ICM to coil does route through ignition switch per the wiring schematics I have looked at. That additional resistance could indicate an issue with the ignition switch itself. You could use a short length of wire to make a jumper across the terminals that plug into the back of the switch to complete the circuit without the switch and test the circuit again. If you are near 1.3 ohms again, that would be a good indication that the switch is causing issues.
Dude! You have been so much help with this, thank you. So what you’re saying is have everything plugged in and connected like it should be, then use a wire to jump from one post to the other on the back of the ignition switch?
Wait, I just had a thought. Would I be able to test the ohms on the back of the ignition switch instead of using a jumper wire? If I do have to use a jumper wire, will a larger gauge lower the ohms? I’m just thinking how to have less interference in my results.
What coil part number did buy? There are many coils with different resistance built into them. My thought is if you bought the incorrect resistance coil your pink wire is going to drop the voltage even further than the normal 9 volts.
Wait, I just had a thought. Would I be able to test the ohms on the back of the ignition switch instead of using a jumper wire? If I do have to use a jumper wire, will a larger gauge lower the ohms? I’m just thinking how to have less interference in my results.
I would unplug the connector from the back of the ignition switch to take the switch out of the variables, and jump the 12v+ from battery coming into the switch to the 12v+ going to the coil essentially simulating the key in the run position, if you are getting the 6-9 volts as you should be with the jumper in place that narrows it down to the switch itself. If you are still getting the higher 80 ohm reading, the switch is fine and there is an issue elsewhere in the wiring harness.
And to answer your question regarding bigger gauge and lower ohm rating, yes that is technically true, but the difference would be so minuscule in such a short length of wire that you would need very sensitive meter to even measure the difference. In a similar vein, colder will be less resistance and warmer will have higher resistance, but again unless we are talking extreme temp differences you wouldn't be able to measure it without lab grade equipment.
