Ignition Coil Problem ????
Thread Starter
Pro
Joined: Sep 2012
Posts: 732
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From: the confused state CT
Ignition Coil Problem ????
I'm helping out a neighbor with his 69 vette. We had a problem today with the ignition coil wires on the + connection getting so hot you can't touch them. It is a 350/350 w/a 4 spd, no a/c, standard points ignition system. It only happens with the key on. The car has been recently restored and has about 200 miles on it since the rebuild, it is stock. We could not find any shorted wires and it has a new wiring harness. Also, there are two wires on the + side of the coil, a yellow one that goes to the starter R terminal and the other cloth insulated that goes to the firewall plug, What is the cloth insulated wire for? The wiring diagram that he has shows that it dead ends at the firewall connector.
Thanks Gary
Thanks Gary
Melting Slicks
Joined: Mar 2007
Posts: 2,520
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From: Hinckley OH
The insulated wire is a resistance wire. Points ignitions are provided with less current when running but full 12 volts comes from the R terminal on the solenoid for more power during starting.
I can't answer the question about them getting hot.
I can't answer the question about them getting hot.
Le Mans Master
Joined: Oct 2006
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Just for fun, check the resistance thru the coil. Meter between the + and -. See how many ohms you get. Then check both to ground and to the center. IIRC, you should see 1.2 to 1.5 ohms between the terminals, open to the case and open to the center. As noted above, one of the 2 wires goes to the starter R (outside) terminal and the other is the resistance wire to the IGN or RUN side of the switch.
Melting Slicks
Joined: May 2009
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2024 C3 of the Year Finalist - Unmodified
The resistance wire is a really stupid idea that GM came up with. They used to have a current limiting (aka ballast) resistor in the circuit. Do not leave the ignition key on without starting the engine. If the points happen to be closed...you are going to fry something....either the resistance wire or the points.
Anyhow, if you are experiencing ignition problems, first try replacing the coil with a known good coil. Next step is the primary wire from the coil to the points. Then the points and condenser. Are we having fun yet, or what?
Anyhow, if you are experiencing ignition problems, first try replacing the coil with a known good coil. Next step is the primary wire from the coil to the points. Then the points and condenser. Are we having fun yet, or what?
Tech Contributor
Joined: Jun 2004
Posts: 20,779
Likes: 957
From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
The resistance wire is a really stupid idea that GM came up with. They used to have a current limiting (aka ballast) resistor in the circuit. Do not leave the ignition key on without starting the engine. If the points happen to be closed...you are going to fry something....either the resistance wire or the points.
Anyhow, if you are experiencing ignition problems, first try replacing the coil with a known good coil. Next step is the primary wire from the coil to the points. Then the points and condenser. Are we having fun yet, or what?
Anyhow, if you are experiencing ignition problems, first try replacing the coil with a known good coil. Next step is the primary wire from the coil to the points. Then the points and condenser. Are we having fun yet, or what?
Melting Slicks
Joined: May 2009
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2024 C3 of the Year Finalist - Unmodified
When the ballast resistor fails, you can replace it. When the resistor wire burns, you have to pull the wiring harness apart and replace the wire from the junction block. Nowadays, Lectric Ltd will not sell you a replacement resistor wire. They won't even give you the specs on it. They will only sell you a complete wiring harness for big bucks. To me, it was a stupid idea. Did any of the other mfrs (Chrysler of Ford) use such a stupid idea? It was obviously a cost-cutting idea from one of their brilliant engineers. Unfortunately, it has not saved any of us a damn thing.
Last edited by Faster Rat; Jul 12, 2013 at 10:53 PM.
Melting Slicks
Joined: Jun 2006
Posts: 2,071
Likes: 147
From: S Nevada
Yes, it was a stupid idea with the resistance wire. My 72 had a ballast resistor installed in place of the resistance wire. The previous owner was probably burning up points and took an idea from Chrysler. I took it further, I'm running an Msd distributor, 6a, and blaster coil.
Tech Contributor
Joined: Jun 2004
Posts: 20,779
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
When the ballast resistor fails, you can replace it. Yes. And that's convenient because they fail at a not-insignificant rate. All the power dissipation and attending heat is concentrated in one small area of that resistor (hence the need for ceramic packaging), and that's a recipe for failure. When the resistor wire burns, you have to pull the wiring harness apart and replace the wire from the junction block. How often does the resistance wire fail? I have never known of anyone having a failure of the resistance wire (YMMV). The fact that the resistance heat is spread along a long path (instead of in a small area) means lower temperature per area, and a resulting increase in reliability. Nowadays, Lectric Ltd will not sell you a replacement resistor wire. They won't even give you the specs on it. So what? Buy it elsewhere. It's just a piece of resistance wire. It's not rocket science. They will only sell you a complete wiring harness for big bucks. To me, it was a stupid idea. Others, with more training in Electrical Engineering, will disagree with you. Did any of the other mfrs (Chrysler of Ford) use such a stupid idea? It was obviously a cost-cutting idea from one of their brilliant engineers. I'm detecting a chip on someone's shoulder. Unfortunately, it has not saved any of us a damn thing.
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Melting Slicks
Joined: May 2009
Posts: 3,079
Likes: 314
2024 C3 of the Year Finalist - Unmodified
Opinions are like you know what. Everyone has one. Every time I look down at the frayed cloth insulation wrap on my $185 Lectric Ltd replacement wiring harness resistance wire, I feel like puking.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,112
From: Crossville TN
If the car was restored, what ignition system does it have? [points or electronic]
What type of coil is on the engine? [stock equivalent or aftermarket "Hi-Voltage" type coil]
What wiring did you use? [stock type w/resistor wire, 'plain' wiring, or don't know]
What type of coil is on the engine? [stock equivalent or aftermarket "Hi-Voltage" type coil]
What wiring did you use? [stock type w/resistor wire, 'plain' wiring, or don't know]
Thread Starter
Pro
Joined: Sep 2012
Posts: 732
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From: the confused state CT
Thanks for the info guys. This happened when the car stopped running and the key was left pn for a couple of minutes. It shut down like you turned the key off. I am getting 12v at the resistance wire with the wire disconnected from the coil. It is a stock points system. It does not happen when the primary wires are disconnected from the coil.
Melting Slicks
Joined: May 2009
Posts: 3,079
Likes: 314
2024 C3 of the Year Finalist - Unmodified
Thanks for the info guys. This happened when the car stopped running and the key was left pn for a couple of minutes. It shut down like you turned the key off. I am getting 12v at the resistance wire with the wire disconnected from the coil. It is a stock points system. It does not happen when the primary wires are disconnected from the coil.
When testing my distributor on a Sun machine, it was determined that the reproduction wire (supplied by Paragon) from the coil to the points was defective. Who woulda thunk?
If you think your resistance wire has given up the ghost, try jumpering the coil to full battery voltage...at say the horn relay. Just don't run it there very long or you will burn your points. If you feel like replacing the points, also replace the capacitor.
