Last weekend while backing in to my parking space at a large cruise-in my '72 of 20 years just died and when I say died I mean died as if someone turned the ignition switch off. I had been barely moving for quite some time and though the engine temperature was crawling towards 210° the engine was performing adequately. This was one of those engine kills that you know there's no amount of cranking that's going re-fire the engine. It was just dead. The car was basically able to coast into the parking space and I began to try to figure out the situation.

I very much felt like this was an ignition issue and as I began too look around I put my hand on the coil and it was extremely hot. Hot as in touch it for more than a second and your skin would have been burned. I checked for spark and if there was any it was very weak. I decided to walk around for a while and let the thing cool off before looking any further. When I came back the engine had cooled somewhat and it immediately fired right up. Thinking the coil was damaged I got a new coil and made the change. I was quite disappointed to find the new coil was smoking hot after what was likely a 5 mile drive. The thing was I had 65 more miles to go and it was getting dark. I made it home without incident and checked the coil again. You guessed it super hot.

My question is where would a person start to figure out what the issue is? The wiring harness is original and largely undamaged but I believe someone has been messing around in the distributor area. Any help is certainly appreciated. I'll post a picture of the distributor/coil soon.

 

The ignition system is all stock.

 

After the car starts and is running the power to the coil (+ side) comes through a resister wire when key is in the run position Test the voltage at the coil when the car is running ( test positive on coil and ground the other lead). Should be around 9 volts. Next I’d check the resistance of the coil wire from the coil to the center of the distributor. I’d try these easy checks first.

 

Is the bottom of the coil touching the intake manifold?

 

I owuld do what was suggested above and trace out those wires that you have conected...none look stock, no telling whats going on there. How long have you =had this and isthis the first time you ever touched the coil after a drive....this could have been going on for quite some time and you just never realized it

 

Before I made mention of what I thought the problem is I wanted to get some input from the forum.

Though the wiring harness is largely untouched, as you can see the wire from the “R” side of the solenoid has been replaced all of the way from the solenoid to the + side of the coil. The black from the distributor to the distributor to the - side of the coil has had a new end put on it. I believe the resistor wire has been replaced or modified from the distributor to who knows where. I simply haven’t gotten that far yet.

After doing some research I mistakenly thought the resistor wire was between the R side of the solenoid and the + side of the coil but have since found out the resistor wire is between the - side of the coil and the bulkhead connector. Does anyone have a picture of what the wire should look like?

I have read several resistor wire threads but haven’t seen what a damaged resistor wire can be replaced with. Any help with that is appreciated.

 

I suspect this has been going on the entire time I’ve had the car but the car is as reliable as the sun so I didn’t have any reason to question its operation.

one of the first things I checked was the coil’s proximity to the intake. There is an air gap so no problem there.

 

Your post got my attention cause I had similar issues with my 72 when I bought it 30 years ago. I refreshed the engine bay at that time and replaced many parts just because I wanted a new baseline. I had a situation where after driving and it got hot the engine would just die. Couldn't figure it out. All new ignition parts including the coil. I finally swapped out the new coil for the old coil (factory a.c. delco) Problem solved. Drove the car many years with no problems except once, when my resistor wire to the coil became disconnected. How does that happen. Well it didn't really become disconnected, my resistor wire had been cut by somebody at one time and a regular piece of wire (about 4 inches) soldered on to extend it to the coil. Not knowing better. I resoldered it. Again car ran great for years. One day I noticed the resistor wire smoking a bit. Wire was so hot i could not hold it. From what i learned the resistor wire should not be cut and extended. The length of the wire is specific and calculated to cause the voltage reduction to 9 volts. If shorter this upsets the calculation. You are right new resister wire is not readily available, plus it should be changed as one complete piece with a specific length from the junction box on the firewall. The smoking worried me. Who knows how long it went on. I decided to just changeover to a petronix III points to electronic ignition module that uses 12 volts that I've taken from the IGN terminal on the fuse box. Sorry long story but thought I'd share. Maybe my old factory coil just could handle the extra voltage who knows. New one couldnt that's for sure.

Is your modified resistor wire hot to the touch when engine running?




.

 

Do you still have points and condenser or is something else in the distributor?

 

easiest is just add a dodge ballast resistor to the main coil wire.

 

That's absolutely wrong. The resistor wire connects to the "+" side of the coil along with the non-resistor wire coming from the starter "R" terminal. The wire going to the distributor/points connects to the "-" side of the coil, and provides a ground path for the positive side of the coil with the 2 wires attached.
Lars

 

Good catch Lars. Didn’t even notice that comment. Yes. Resistor wire to positive on coil. Should be three connections to positive on coil. At least on my car. Hot from starter when key in start. Resistor wire hot when in run position. Last item not critical but capacitor for the radio. On points set up. Only one wire from negative on coil to distributor. Keep us posted on the outcome.

 

Yes, stock, points ignition.

 

I've been visually inspecting the wiring to see if anything has been damaged. So far it doesn't appear anything has. I'm reassembling everything and when I get a battery cut-off will resume testing.

 

Just so I'm clear the resistor wire does not exist between the + side of the coil and the R side of the solenoid. The resistor wire does exist between the + side of the coil and the ignition switch?

 

Correct.

 

Thanks for the help.

 

Just out of curiosity, could an overcharging alternator cause this situation? While on my way to and from that cruise-in the needle on the ammeter was approximately a gauge needle's width to the right of the zero mark on the ammeter gauge.

 

you need to use a voltmeter but would expect bulbs to burn out and I thought it was already established you are missing the resistor wire. Have you looked at the points to see if they are burnt?

 

frm what I could find in a brief search is this coil will function from 9 volts to 14 volts if its a factory good coil. I have read that there are bad batches of MSD coils from their suppliers. So the voltage shouldnt be an issue of why this is getting hot. I would do the resistance ohm readings and see if its within specs...maybe its under voltage and thats why its getting hot much like a motor that is running on too little amperage and it overheats due to working to hard to get the amperage it needs