Resistor wire question
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Elder User
Joined: Nov 2009
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From: Mayfield, KY
Resistor wire question
So I have been doing some wire rerouting under the dash and I notice this "pink" looking wire from the ignition switch to the firewall. I've got a resistor wire, nothing strange......but, my truck has a stock resistor coil as well. I asked my dad about it and he said he had to special order that from Ford many years ago when the original resistor coil went bad. He had no idea about the resistor wire in the cab so I wonder would this cause any problems with getting a good strong spark at the plugs? I figure it got put on the truck by accident at the factory as I can see no reason to have both....
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Elder User
Joined: Nov 2009
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From: Mayfield, KY
I forgot to mention this truck was bought new by my uncle and traded to my grandfather within a year. Nobody has ever worked on it but my father except for alignment until I got it in 99. It appears to have come this was from factory.
Hotshot
Joined: Mar 2013
Posts: 14,255
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From: Phoenix, Az.
Sounds like back in the day someone put Ford's after the factory "transistorized ignition" kit on this truck. Ford had an add-on kit much like the current pertronix. Then someone might have put the points back in it but left the different coil. If you got 12V on RUN then leave the coil there.
Hotshot
Joined: Oct 2002
Posts: 18,488
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From: The Big, Oregon
You will get 12v at the coil with the points open whether it has a resistance wire or not. No load, no resistance.
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Fleet Mechanic
Joined: May 2001
Posts: 1,396
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From: Cupertino
Exactly as above. Pop the distributor cap, manually rotate the crank until the points close. Then, normal would be 7-8 volts if the pink swamping wire is intact.
If you don't get that, report back.
If you don't get that, report back.
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Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
Hey guys, I thought the load is the resistance built in to the pink resistance wire if it is intact. The 12V running through the resistance wire should be cut down to 7 or 8 whether the points are open or closed I thought. What am I missing?
Fleet Mechanic
Joined: May 2001
Posts: 1,396
Likes: 4
From: Cupertino
The points are a switch. If they are closed, current flows from the ignition switch to ground, through the points.
If the points are open, no current flows, there is no voltage drop across the resistance (pink) wire. You read battery voltage at the top side of the coil.
If the points are closed, current flows. The resistance of the coil primary and "pink" wire are about the same so there is a voltage-divider situation. Ohm's Law splits this drop between the resistance wire and the drop in the primary resistance of the coil. Each gets half. Hence six or seven volts at the top side of the coil with the points closed. 12 volts with the points open.
Semper Fi
If the points are open, no current flows, there is no voltage drop across the resistance (pink) wire. You read battery voltage at the top side of the coil.
If the points are closed, current flows. The resistance of the coil primary and "pink" wire are about the same so there is a voltage-divider situation. Ohm's Law splits this drop between the resistance wire and the drop in the primary resistance of the coil. Each gets half. Hence six or seven volts at the top side of the coil with the points closed. 12 volts with the points open.
Semper Fi
Last edited by CougarJohn; Jan 27, 2014 at 04:35 PM. Reason: I messed up
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
The points are a switch. If they are closed, current flows from the ignition switch to ground, through the points.
If the points are open, no current flows, there is no voltage drop across the resistance (pink) wire. You read battery voltage at the top side of the coil.
If the points are closed, current flows. The resistance of the coil primary and "pink" wire are about the same so there is a voltage-divider situation. Ohm's Law splits this drop between the resistance wire and the drop in the primary resistance of the coil. Each gets half. Hence six or seven volts at the top side of the coil with the points closed. 12 volts with the points open.
Semper Fi
If the points are open, no current flows, there is no voltage drop across the resistance (pink) wire. You read battery voltage at the top side of the coil.
If the points are closed, current flows. The resistance of the coil primary and "pink" wire are about the same so there is a voltage-divider situation. Ohm's Law splits this drop between the resistance wire and the drop in the primary resistance of the coil. Each gets half. Hence six or seven volts at the top side of the coil with the points closed. 12 volts with the points open.
Semper Fi
Posting Guru
Joined: Mar 2006
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no worries- i don't have one either.
long story short- if the circuit isn't completed (points closed), you can't read the resistance. it'll just show battery voltage.
so- you should always measure the circuit with the truck running- or, you can run a jumper wire to ground the negative side of the coil. anything that will complete the circuit.
my eyes bugged out the first time someone explained it to me- its a hard thing to grasp if you're not an electrician, i guess.
Fleet Mechanic
Joined: May 2001
Posts: 1,396
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From: Cupertino
Jefa, ohmeters don't care about + or - leads. They read resistance. You must disconnect the battery before doing any resistance checks. Or, you will blow the meter movement.
The guy above gave a pretty good explanation, methinks.
The guy above gave a pretty good explanation, methinks.
Hotshot
Joined: Mar 2013
Posts: 14,255
Likes: 199
From: Phoenix, Az.
WOOPS! I did type ohmeter but meant to say Multi-meter. I guess I got to slow down before I hurt myself! LOL! Set to volts, not resistance. Sorry John for the confusion. But I meant positive lead to the pink wire and grounding the negative wire of the Multi-meter.
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