I needed to remove the original (or a very old aftermarket) 6 volt coil from my 41 Series 78 to do some electrical testing and came across this very unique and cumbersome design which makes removal of the coil a rather painful exercise. I am posting in case is helpful to other owners of antique GM cars. I found out that Pontiac, Cadillac and Olds have these unusual coils that protected the ignition wire with a cap, presumably as an anti-theft device. My 41 shop manual gives a two line description how to remove the cap which is necessary to reach the electrical connection. It says "use tool J-726 to release the lock and then rotate coil clockwise and cap counterclockwise". I could not find even one photo of this tool but seems is a metal blade to be inserted between the cap and the body of the coil. I want to show the trick needed to release the locking mechanism. Without it you can spend hours like I did until you can figure it out. I could not identify any clear instructions visiting various forums either.

The first photo shows the coil hanging from the ignition wire after I removed the bracket from the firewall. It has no marks of any kind to show where the lock is. The coil is kept very close to the firewall to the point that in order to work on it you first have to loosen up the ignition wire at the ignition key so the coil can be separated several inches from the firewall.



The next photo illustrates the improvised tool J-726 (feeler gauge 0.020 worked for me) and the angle at which you have to aim it. The manual says to insert it about an inch from the ignition wire on the RIGHT side. Most car guys will think that the R side is the passenger side but in reality the lock is on the driver's side as you can see in photo. The feeler gauge has to be thick enough to have strength as you insert it between the cap and the body. Its purpose is to separate the indentation seen in the photo from a detent that is found on the cap at that level, a small metal peg that is visible in a later photo. I used all sizes of feeler gauge starting with 0.006 up to 0.025 but for some reason it was 0.020 the one that released the detent.




Next photo shows the cap. Notice the detent that fits into the indentation and 2 small lugs that project and slide into the openings of the coil body. The sliding may be possible if the cap is not all fixed to the body from old age like mine was. In that case you can turn the body of the coil clockwise (looking from below) and the 2 lugs slide away. Mine was stuck and I had to tap and hit with hammer and some force until it pop open. Of course, all was done guessing, multiple trial and errors as I had no knowledge of what this cap looked like inside.


Locking mechanism: Detent in cap

You will also notice that the cap can not be removed from the car to have a conventional coil installed unless you cut the ignition wire which is soddered to a ring attached to the positive stud. Of course, unless you find an original replacement coil and just re-use the same coil cap.

Hope this is helpful. Manuel

 

Super write up! Thanks for helping others

 

Thanks for the info.... Learned something new.... Tedd

 

Excellent write-up, Manuel.