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Pos. ground coil

Started by Don Boshara #594, July 31, 2009, 12:32:59 PM

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Don Boshara #594

I just read "The Cadillac Serviceman" of October 1947 that said, "Under no circumstances are the two types of coils interchangeable" when referring to negative & positive ground coils. My '40 has been running 26 years with the wrong coil and no ignition problems . When am I supposed to start worrying?
1940 Sixty Special
1966 Mustang Cpe

Dave Shepherd

Coils operating with reverse polarity will still run an engine, available spark under load conditons is reduced, probably not much of an issue with older lower compression engines.

Doug Houston

Don't worry at all, if you're happy. The polarity of the center electrode of the plug is supposed to be negative. Coils are wound so as to make this hookup when installed in the car.

Unfortunately, good, or NOS coils are tough, or impossible to get for our Pos ground cars. I've bought a new epoxy cast coil for one of my cars, and it works very well. If I were to connect the promary otherwise, the engine would not run smoothly, not with decent performance. Starting is also degraded.

I've gone through this drill with several of my cars, and it's the same story. The wrong coil doesn't work properly. Engine performance is lousy the wrong way.

You might want to get hold of a coil, where all terminals are out in the open, and connect it so as to produce the correct spark polarity, and see if the engine runs better for you. You can use a regular replacement 12 volt coil, as they operate on about 8 volts in regular operation. They work like the blazes on 6 volt cars.
38-6019S
38-9039
39-9057B
41-6227D
41-6019SF
41-6229D
41-6267D
56-6267
70-DeV Conv
41-Chev 41-1167
41 Olds 41-3929

Ted in Olympia WA

You would think that with all the Ford cars and tractors made a positive ground coil would be easy to find.  Or does the Cadillac coil look different than a regular coil?

TED
Selling used Eldorado Parts from 1971-1978.  Member Number 25659.

Doug Houston

The fact is that most of the cars built before WW II, had positive grounded systems. Indeed, Ford and Chrysler Corp. cars had + grounds. The design of the ignition coil HOUSING was the fly in the ointment here. The coil that most GM cars used, had a locking cap and an armor for the coil wire, going into the ignition switch. Note that in General Motors, Cadillac was the only one to have a positive ground before WW II.

Coils used by others, such as Ford and Chrysler couldn't be properly mounted on a Cadillac. For instance, Chrysler's (Auto-Lite) coil mounted woth a flange, as it passed through the firewall  Ford's pre-WW ii coils were mounted on the distributor on the front of the engine, and resembled no other coil. (Ford's coils were the hottest ones used on passenger cars then)

Almost any Delco coil can be used on a Cadillac, with some exceptions. Buick and Chevrolet had special coil moiuntings or terminations, so that kicks them out. Oldsmobile also had a coil that wouldn't mount in a Cadillac. I'm not sure of Pontiac. But, there are lots of postwar Cadillac coils around, and also scads of Delco replacement coils that have an attachable top cap for the armor termination, but they all seem to be for negative ground systems.
38-6019S
38-9039
39-9057B
41-6227D
41-6019SF
41-6229D
41-6267D
56-6267
70-DeV Conv
41-Chev 41-1167
41 Olds 41-3929

TJ Hopland

Any photos of what these cadillac coils looked like?   The ones I remember were pretty coil looking like and like Ted was thinking there seems to be plenty of tractors and other industrial motors still around.   I may just not have seen the style in question.    I do remember the ones in the firewall.  Was that to try and keep them cool?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Bill Ingler #7799

Here is a picture of a 1946-47 Cadillac negative ground coil showing the lock type extension at the bottom of the coil. The positive ground coil 1115128 as used on the Cadillac in 1939 through 1942 is very similar to the picture except the 115128 had the top ring collar somewhat smaller and as well as the bottom collar. 1115128 as well as Delco-Remy were embossed on the side of the coil and had the lock type extension on the bottom of the coil. I have seen 41 Cadillacs with a 1948 Cadillac 1115380 negative ground coil mounted on the firewall. Wires are reversed to make it work, the armored cable can`t be connected and the firewall looked like crap. The Cadillac positive ground coil is a hard one to find. There is a company making a copy which can be used with the armored cable and lock. Expensive yes but so is  1115128 if you can find it.
http://atwaterkentmfg.com/index.htm

Don Boshara #594

Thanks to all of you for the information. I'll check with Atwater Kent for their price. Hope it's less than the GM bailout.
1940 Sixty Special
1966 Mustang Cpe

herman

How does one tell from looking at the coil if it is positive or negative ground?  I have tree Declo Remy coils and noe have anything to mention whether they are + or -.  Any hints

Herman

Bill Ingler #7799

Hi Herman: About the only way I can tell without the + or- at the top of the coil is to take the number embossed on the side of the coil and look in my Delco parts books and see what car used that coil. To check if that car was a positive or negative ground I then look at what Delco regulator was used on that car. I take the regulator number and go to a Delco test specs book and it will tell me if that regulator was used on a positive or negative ground. A round about way that works sometimes. I always thought that whomever designed the Delco numbering system had an elevator that never went all the way to the top. Post or email me direct the numbers embossed on the sides of your coils and I will attempt to tell you what car used those coils.

herman

Bill

Thanks

The + and - are embossed on the top of the coil...so is that all that matters?  There are no numbers on the coils that I have.  So how does one tell if it is 6 volt or 12 volt?  Or does that matter?

Herman

Don Boshara #594

This could help or add to the confusion.
1940 Sixty Special
1966 Mustang Cpe

Bill Ingler #7799

Hi Don: That was a good way in 47 of telling the difference between the 42 and the 46-7 coil. I believe the coils that were placed on the car at the factory had the mounting bracket spot welded to the case and so they came up with this to make sure the positive and negative coils were not mixed up on 42 or 46/7 cars back at the dealers. Of all my years walking the flea market at Hershey I have never found  NOS Cadillac coils used on positive or negative systems that did not have separate mounting brackets. Another strange quirk of Delco-Remy is their marking of their replacement box for new Cadillac coils. 1115128 used on 39-42 Cadillac is marked that way on the box as well as embossed with that number on the coil. NOS Delco coils for 46-47 Cads as shown in the Delco-Remy catalog will be marked 1911441 on the box but the coil inside will be marked 115351.

Herman: Yes the plus and minus at the top of the coil is the key to getting the correct polarity to the plug. As Doug pointed out in an earlier response, negative polarity always to the plugs,regardless of how the battery is grounded. I have tried over the years to buy NOS in the original box so I would know if it is 12 volt or 6 volt. Looking at 2 orphan unmarked coils side by side to determine 12 or 6 volts- beats the H out of me how you can tell the difference. There is an old mechanics way of testing to see if you have the correct polarity to the plugs. With the engine running,disconnect one of the spark plug leads from a plug. Hold that lead about 1/4 inch from the plug terminal and place a sharpened end of a lead pencil between the spark plug lead and the plug. If the spark jumps between the pencil and the plug you have the correct polarity. If it sparks between the plug wire and the pencil than you have incorrect polarity.


Wayne Womble 12210

Just be careful when dealing with Atwater Kent. Thats all I`m going to say.

Tom Beaver

Bill: Would you happen to have any information on a Delco Remy coil #1115403?  It came with my 38 LaSalle and has the locking ring for the armored ignition cable.  I did a test start of the engine with it and it worked but now I wonder if it really is a positive ground coil.  I did a search on the internet but didn't find anything.  Any help would be most appreciated.

Tom Beaver

TJ Hopland

I was helping a friend get his 50 nash running last weekend.  It uses delco electronics.  The manual said that the positive ground regulators have copper armatures and the neg ground ones are cadmium (which I assume is silverish?).   We did not have any coil issues so I did not look close at that section of the book to see if it said anything about identifying the coils.
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

Bill Ingler #7799

Tom: I looked through all my Delco books and did not find 1115403 used on any named car or truck. As I pointed out in another posting, Delco would put a number on their box but the coil inside carried a different number. Chevrolet had 1910405 on the box but 1115401 inside. The only place I found reference to your 1115403 was in the Delco specs book. That did not give me a clue as to positive or negative. I will make an assumption that your coil is negative ground based upon what Doug Houston said in his above post that the GM used the unique locking cap for the coil connection and the only GM car to be positive ground before WWII was Cadillac. 1115128 was the coil used by Cadillac for positive ground and as far as I know Delco never made a substitute positive ground coil for the 1115128. 1115403 was probable used as a substitute used by another negative ground GM car. If works for you then stay with it.

Tom Beaver

Bill:  Thanks for your reply.  I was afraid that the coil probably was negative ground knowing what other things the previous owner did to the car.  When I am able to fire it up again I will try your pencil test to see if I can verify your prognosis.  And in the mean time I will look for a 1115128 coil.

Tom Beaver

bcroe

The positive or negative ground issue is a matter of which way the windings are connected.  Like any transformer, this can be measured on the bench, probably someone has already written this up.  Say, put 5V 60 HZ on the primary, a 1000:1 attenuator on the output, observe if attenuator output is in phase or out of phase with input.  A scope is best, but a meter would work.    Turns ratio would probably reveal 6V or 12V coil.  Bruce Roe CLC # 14630