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From: I'd like to propose a toast... to internal combustion and wind in the face.
Note the connector in the black wire that joins the red wire that attaches to the coil:
Now, note the same type of connector with the tan wire going in and the black wire going out. This picture was taken at the bulkhead connector.
The connectors connectors look very much the same which makes me wonder about what color the resistor wire should be. The car is a ‘72 454 with air, PW, PB.
Here is a 1972 Corvette wiring diagram.
It clearly shows 2 wires off the coil + one as yellow going to the starter, and one as black-pink going to the bulkhead.
From those pics. My guess is that the resistor wire has been removed.
Turn key to ON. Is the coil voltage steady at 12 volts? If so, wire has no resistance. So straight 12v.
If 12v, this is what I see. Hard to tell though in pics Somebody has tapped into a tan wire to get 12v hot to the coil while key is in ON position. Hard to tell which bulkhead connector I’m looking at, but one has two tan wires per wiring diagram. One that feeds the wipers and the other the TCS solenoid. Both of these are hot I believe when key is ON. A lot of people tap the wiper motor for 12v hot for ignition conversions.
You're TCS still being used?
If your resistor wire is indeed gone. You have options. Complete New wire to bulkhead (to keep points), use a ballast, convert to 12v electronic ignition.
I have another wiring diagram that shows wire gauge numbers. Attached.
From: I'd like to propose a toast... to internal combustion and wind in the face.
I've got everything reassembled but because I scare myself when I start messing around with anything electrical I'm not connecting the battery until I get a battery cut-off switch. I'll start measuring voltages then.
The TCS is not hooked up.
Thanks for all of the help. I really appreciate it.
I quickly read through your thread and didn’t see this one thing mentioned so I’ll chime in.
Coils which are “starting to go bad” will test and function good when they are cold.
As they are heated by engine heat they will fail under test.
Its not uncommon to have a coil that functions as it should and fail when heated up.
I’ve seen coils that will fail on a warm engine and function normally once the engine and coil cools.
Your coil may have been failing and totally failed when your engine heat raised, but tested normally on the bench at home.
A new coil may be all you really needed to get back on the road.
It is nice that you had to take the time to get the wiring corrected.
It’s possible that a prior owner swapped out the points distributor for a non points distributor, which would require the removal of the resistance wire and it was never properly replaced when the points distributor was put back in.
I quickly read through your thread and didn’t see this one thing mentioned so I’ll chime in.
Coils which are “starting to go bad” will test and function good when they are cold.
As they are heated by engine heat they will fail under test.
Its not uncommon to have a coil that functions as it should and fail when heated up.
I’ve seen coils that will fail on a warm engine and function normally once the engine and coil cools.
Your coil may have been failing and totally failed when your engine heat raised, but tested normally on the bench at home.
A new coil may be all you really needed to get back on the road.
It is nice that you had to take the time to get the wiring corrected.
It’s possible that a prior owner swapped out the points distributor for a non points distributor, which would require the removal of the resistance wire and it was never properly replaced when the points distributor was put back in.
One quick simple test is to check the cranking voltage at the coil.
You should see about 10.5 to 11.0 vdc at the coil when the engine is cranking over and only during cranking.
Just remove the coil wire going to the distributor so the engine won’t start and have someone crank the ignition while you monitor the voltage.
The resistance wire was put in place to protect the points during cranking of the engine.
Without cranking you should see battery voltage at the coil.
If someone at some point replaced the oem points and went to an electronic ignition setup, the resistance wire should have been removed because an electronic ignition system requires 12 vdc during cranking otherwise you are getting a week spark.
If you plan to keep the points distributor (which is a really great system) then replace the resistance wire and wire it per the factory wiring schematic.
But first replace your coil!
Its not uncommon to have a coil that functions as it should and fail when heated up.
I’ve seen coils that will fail on a warm engine and function normally once the engine and coil cools.
Your coil may have been failing and totally failed when your engine heat raised, but tested normally on the bench at home.
.
I'll second that old car burn. In post 8 I kind of explain the same issue you discuss but not as well as you. Had new coil. Faulty. My father in Law had similar coil hot short run issue on a 59 vw bug. Had he not mentioned it I would not have suspected a new coil. But cause my resistor wire was modified/spliced the higher voltage (not smart enough to know back then - before forums lol) may have stressed the non gm coil. I replaced it with the old factory unit and no issue for many years until i noticed a Hot resistor wire and coil. This caused me to worry of fire so i decided modify and correct the whole ignition run mode set up.
Rookies thought: Crimp-On connectors joining two wires of different colors in the Ign. System (as other members mentioned).......not a good sign.
It's a good thing mudbone. is rewiring it correctly this time
(my '68 basket case Ign. was modified at least 3 times)
When I began troubleshooting the '68 Ign wiring as a rookie Tylenol was my friend
Key On = 13V Good so far (Prev. owner removed Points distributor and installed HEI distributor)
After 2 hours of driving engine stalled........found 4V at HEI distributor connection-he had cut off most of the original cloth-wrapped resistor wire and then crimped on 16ga. wire from firewall to distributor connector. From there....it got worse
Take pics of your new wiring when it's finished with explanations so the expert members can verify what you have done
From: I'd like to propose a toast... to internal combustion and wind in the face.
I suppose I mentioned it earlier but I've had this car for over 20 years and this is the first time I've detected this problem. There was one other time that I had driven the car about 15 miles and it just died. However, after it sat for a matter of seconds it re-fired and I kept on driving another 10 miles to my destination. Not long after that I was taking another drive where after about a mile it died again and would not re-fire even after setting for 2-3 hours. A new set of points seemed to cure all of those problems. Now, about 20 years later here I am. I'm going to perform the diagnostic tests before opening up the wiring harness.
First thing I would do is throw on a new oem type coil.
Start it up and see how it runs.
It may be all you need to correct the issue.
Coils are cheap and you can swap one in about 10 minutes.
If that corrects the immediate issue, then you should look into making the wiring connections correct per factory specifications.
Just my $.02 worth.
Not long after that I was taking another drive where after about a mile it died again and would not re-fire even after setting for 2-3 hours. A new set of points seemed to cure all of those problems. Now, about 20 years later here I am. I'm going to perform the diagnostic tests before opening up the wiring harness.
"New set of points cured the problem". A clue I would think. The reduced voltage from the resistor wire is required to prolong the life of the points. 12 volts to the coil will fry points over time. Your planned voltage diagnostic test while in the run position will determine either: new resistor wire connection needed or another coil. But then its electrical! Lets be positive Process of elimination. Lets see what your testing shows up. You'll get it figured out.
From: I'd like to propose a toast... to internal combustion and wind in the face.
Originally Posted by Dino_'72
"New set of points cured the problem". A clue I would think. The reduced voltage from the resistor wire is required to prolong the life of the points. 12 volts to the coil will fry points over time. Your planned voltage diagnostic test while in the run position will determine either: new resistor wire connection needed or another coil. But then its electrical! Lets be positive Process of elimination. Lets see what your testing shows up. You'll get it figured out.
Given the history of the situation I believe you're correct. I'd be shocked if I've driven the car 5,000 miles in 20 years so it would likely take significant time for an issue to come to lite.
From: I'd like to propose a toast... to internal combustion and wind in the face.
Diagnositc results
Primary side coil resistance:
Old coil: 3.5 ohms (I think this is out of spec)
New coil: 1.6 ohms
Secondary side coil resistance:
Old coil: 8.25k ohms
New coil: 8.6 ohms
Voltage at battery: 11.96 volts
Key in "off" position voltage at coil: 0 volts
Key in "on" position voltage at coil: 11.9 volts
Key in "cranking" position voltage at coil: 8.6 volts
*All voltage values were measured with new coil
The battery is in good condition and the engine sounded as if was cranking over like it typically does so I am a little surprised at the cranking voltage. Otherwise, that coil? Yea, she'd be runnin' a little bit hot tonight.
Primary side coil resistance:
Old coil: 3.5 ohms (I think this is out of spec)
New coil: 1.6 ohms
Secondary side coil resistance:
Old coil: 8.25k ohms
New coil: 8.6 ohms
Voltage at battery: 11.96 volts
Key in "off" position voltage at coil: 0 volts
Key in "on" position voltage at coil: 11.9 volts
Key in "cranking" position voltage at coil: 8.6 volts
*All voltage values were measured with new coil
The battery is in good condition and the engine sounded as if was cranking over like it typically does so I am a little surprised at the cranking voltage. Otherwise, that coil? Yea, she'd be runnin' a little bit hot tonight.
you have no resistor wire since you have battery voltage with key in on position. Fully charged battery should be 12.75.
Resistor wire will start out at 12 volts and then drop down to about 9 volts or so. I would get a helper and go from off position to the “on” position. Watch your voltage meter and Measure voltage over say 45 seconds after you turn it on. The resistor wire will start doing its thing and start dropping the voltage during this time. If no drop, you are running 12 volts steady with key on. Not point or coil friendly as discussed earlier. All things pointing to as are the pics to no resistor wire present in your ignition system.
