Since the coil is painted, and most brackets are painted, I can't see how they have any chance of obtaining a good ground.

 

Nope. The bottom of the laminations of the secondary are isolated from the case by a porcelain insulator, and at the top by the dielectric material that forms the cap. No electrical components inside the coil are in contact with the case.

 

I made the mistake of arguing this point once before and had to go back to the books and research the topic. I hadn't had time to post my findings in the previous thread about this but now it's time.

JohnZ is absolutely correct concerning the internal configuration of the AC coil used in the 60's on the Corvette and other GM cars.

Jim_C is correct for coils used on some British, Italian and earlier GM vehicles. I reference a couple on-line books of automotive history: Hillier's Fundamentals of Motor Vehicle Tech, by Victor Albert and Walter Hilliers, Motor Vehicles and Their Engines, by Edward Smith Frasier, and Automotive Ignition Systems, by Earl Lester.

Browse these books and you will find that there are various internal configurations used by the automotive industry. Cadillac for example used a coil with the secondary isolated from the primary and connected to case ground. I found coils with common + connections (GM) and common - connections (Chrysler).

I was intrigued by these different configurations and researched the pros and cons of each. The common + configuration (referenced in one of the books as Earth Return but I suspect the ER designation is referencing ElectromotiveForce (Voltage)*Resistance) is what was used on our Corvettes. In analyzing the active circuitry of the primary and secondary ignition systems using this design, I found that the energy of the secondary system returns to the coil through the battery. If the resistance of the sparkplug decreases, the battery has to absorb the extra energy the plug didn't use. Also, if the battery is disconnected while running, the return energy is through the alternator and the diodes of the alternator are subject to any extra energy left over from firing the sparkplug. The advantage is a reduction of one connection to the coil.

The common - configuration (referenced as IR or Intensity (current)*Resistance) was used on some Chryslers. This design puts both the energy of the primary and secondary windings in series and increases the net energy output of the voltage available at the plug. Besides the issues of the battery being in the return path, the down side is that additional energy has to be held in the condenser.

The isolated secondary coil, which is used on most modern ignition systems and some 60's era vehicles (along with many other applications) isolates the primary circuit from the secondary. This reduces the effect of the return energy passing through the battery. The down side is to increase output, additional windings in the secoindary are needed so it costs more to produce.

The isolated secondary type coils that use the same cylindrical design as other ER or IR coils, need good contact to the outside of the coil. I have a 67 Fiat and the Bosch coil it uses has the secondary connected to case as Jim_C describes. The mounting bracket has a dimple in the side of it to bite through the paint on the coil to make a good connection.

I'm sure that there are more pros and cons to each design, but my intention is to let everyone know that these designs all existed at the same time and are the reason there are so many different understandings of coil design.

 

Like rgs said, it seems there were some coils with a grounded case. This picture is from a book about electrical systems published in the 70's. Figure 57. I just can't figure out how the bulb could light.

 

This has been a good thread about how the ignition system works in our cars and "69427" has described it quite accurately. However, the point of the post was coil failures. Heat and vibration are more damaging to coils than the voltage that runs through it. Since your problem appeared after replacing the resistor that is where I would look for your problem. First, how did you test the coil for failure? Are you sure it really is bad? Resistors get quite hot in operation and it may be defective and suffering an intemittent open circuit. New parts aren't always reliable. Try the old resistor again and see if the problem goes away.

 

I have finally completed my testing on this problem. I was getting all kinds of weird readings on my digital meter. Thought I had bad batteries,replaced them and was still getting crazy readings. Turned out the meter was bad. Got a new meter and these are my readings...Ballast resistor 2.6 ohms. Coil primary 2.8 ohms,secondary each side to tower 10,800 ohms. I also measured my the wire from my coil to the distributor and I get .6 ohms. The problem I'm having acts exactly the same as when my original coil went bad a couple months ago. The car was running fine. I stopped at a red light,and when I went to pull away,the car was running terrible. Sounds like it is running on 3 cylinders,will barely reach 30 mph,missing badly and makes a fluttering sound out of the exhaust. The car starts ok.but hard to keep it idling,until it warms up. I'm thinking now, maybe the condenser went bad, even though its a Accell,with less than 300 miles on it. Could this problem be in the firewall electrical plug? The oil pressure and engine temperature are normal,and the problem exist whether the engine is cold or hot. The points are new and look good. I guess I'll replace the condenser tomorrow.

 

see if the condenser is simply just loose in it's mount or not grounded

 

Tight as a drum.

 

Ok, need to add my 2 cents to this quote just to clear up some potential confusion, the OP appears to be describing issues with his 65 model, there was never a resistance wire used in any vehicle that used a ballast resistor. Its just plain wire, covered in pink vinyl insulation.
In TI application it is different and the separate TI harness does have a resistance wire built in, but no ballast resistor is used.
Resistance wire built in to the harness began in 1968.
The ballast resistor was eliminated with that.
Other models may be different on year change over.

Also, the coil case does not need to be grounded to anything in order to function and could hang in mid air and still work, I am sure we all have seen coils mounted to the fiberglass firewall in a retro rod set-up.

Quick thoughts on the coil failures, are there any other circuits attached to the hot side of the coil or the coil side of the resistor?
A voltage source for an electric choke or electric fan?

Is the coil polarity correct?

 

The wire on the neg side of the coil is going to the dist. The 2 wires on positive are blk/pink,and one goes to the bottom of the ballast resistor ,and I believe the other goes down to the starter.

 

OK,
That checks out. Do you have a radio capacitor hooked up to the coil?
Also let us know if there is anything else hooked up to the coil or the ballast resistor.

 

Yes,I have a radio capacitor hooked up at the + side or the coil,and just 2 wires on the resistor. The top wire goes through the firewall, to I assume, the ignition switch,and the bottom wire goes to the + side of coil.

 

Yes,
You are correct on your wire routing, in both posts. The second pink lead on your coil going to the starter soleniod feeds the coil during starter cranking and feeds full voltage to the coil, bypassing the ignition switch and ballast resistor. This ensures full voltage to coil at start.
After starting and the ignition switch returns to the run position it is feeding the 12 volts from the switch (fed by wire described further on )out to the ballast resistor, then on to the coil.

Try disconnecting the capacitor on the coil, see if that is your problem.

There is nothing going thru the firewall circuit for the ignition ALTHOUGH there is the big fat red wire going through that feeds everything on the interior side of the firewall, which includes the ignition switch and the pink wire going back out to the resistor. I cannot tell you how many of those firewall connectors I have seen fail, seems to be more often now. The connectors get dirty, build resistance, which builds heat, which builds more resistance,and on it goes. Carefully pull the connector, ( use catious releasing the locking tabs, its all OLD plastic) use a toothbrush or other light duty brush and clean both sides using contact cleaner, Do not use a brass or metal brush as it may be to agressive.

I have seen instances were this is the cause of maladies you describe.


If all that fails, look at the ignition switch next, when driving, if it starts to "break up", simply jiggle the key in the switch immediatley as its breaking up (you need to be doing it aggressively enough to affect the contacts in switch a turning the key type of jiggle, as if you were turning the switch off but not going that far and back) and if that clears it up, thats your answer, crappy contacts, bad switch.

Yes, I have actually experienced that situation.

The 65 switches are not available as an exact replacement but workable service units are. If you are very handy the 65 switch MAY be repairable, thats another story if needed.

While in both the connector and switch, look for any evidence of overheating, melted insulation or mis-shapen connector body. If you find that in either case you are seeing evidence of high resistance build up at the contacts where the damage is. Very common on these old cars, keep in mind as long as your battery is connected that connector and all the wires under the dash are HOT, meaning +12 VDC even with the ign. switch off. Should be enough to make realize you need to be sure you always disconnect your battery when the car is not in use.

BTW, for some informative reading on wiring and the effects age and ozone have on them, go to Lectric Limited's website and read what they present. No I have no connection with them whatsoever, I just agree with all they have written on the subject.

Keep us updated!

 

Good call Unk.....I had that very thing happen last month - turns out a harness connecter to my ignition switch was split in 1/2 - very odd...and intermittent. Car would start but not run about once a week. Rather than replace the harness I put a big 'gob' of solder on the ignition switch tab to make things tighter and that fixed it....
My first thought when this happened is that is was the coil or the ballast resistor (wrong!)

Definitely worth checking out!

 

Excellent suggestions. I just got back from the store with a new ignition condenser and I'm going to install that and see what happens. I'm starting to lean toward that firewall connection myself. I took both connectors apart about a year ago and cleaned them with contact cleaner and a brush. They actually looked pretty good. Thanks,and I will keep you posted

 

PROBLEM SOLVED! I would like to thank everybody for their help,especially "Uncle 427". The problem was the radio capacitor connected to the coil. I never would have guessed its failure would make my engine run that bad,especially since its brand new,with less than 200 miles on it. Repro part,probably made in China......I should have known. Thanks again Uncle.

 

Yup, when that capacitor goes bad, it shorts to ground through its case, which is electrically the same as the points being closed all the time and never opening; no open, no spark.

 

A "radio capacitor" is hooked to the positive side of the coil, versus the points capacitor, which is hooked to the negative side of the coil. A shorted, or electrically leaky, radio capacitor will just reduce the available current that the coil can "injest", causing a reduction in coil energy and possibly not allowing the coil to be able to generate sufficient voltage to arc the plugs. Regardless, this should not affect the coil health, as reduced, not extra, current is passing through the coil primary circuit.
Conversely, a shorted or leaky points capacitor will cause continuous current to flow through the coil, causing a continuous heating of the primary circuit windings.

 

Great! Whatever worked, glad if I helped. I had to, I own a goldwood yellow 65 conv also!
Bill Caldwell