This 37 Lasalle has the + side of the coil going to the key (which eventually ends up at the - term on the Batt) and the - side going to the points which thru those points gets grounded to +. Because the way the coil's made (long story, just trust me) it can't be wired any other way. This makes no sense to me as it's wired exactly how all my - ground cars are. Is there something I'm missing or is this coil a blem and marked incorrectly? THX
hey if it works don't mess with it... I do know a number of cars were positive ground at this time such as my 41 De Soto. but then again maybe your LaSalle is supposed to be a positive ground. if you decide to try positve ground don't forget the polarize your generator.
I had this in my files and can't remember where I got it and I think it was talking about an MG but the principle applies to all cars and should shed some light on the subject... IGNITION COIL POLARITY - There is some misconception about ignition coil polarity and how important it may be (or not). For most people it is only a matter of lack of knowledge, perhaps followed by getting some bad information. How the coil works (with points and condenser) to create a high voltage spark is covered in another article. This article is a discussion about electrical polarity of the coil and spark plugs. The ignition coil is essentially a low voltage to high voltage transformer with about 100 to 1 ratio of windings and voltage. The coil case is not grounded, and both primary and secondary windings inside are "floating" or isolated from the case. The only thing the windings have in common is one end connected to the same primary terminal, and it really doesn't matter much which one. Being a transformer it must have pulsating or alternating current to work. Initial pulsating is done by connecting and disconnecting the primary circuit ground connection. Alternating current then comes into the function in a big way by electrical "ringing" in the condenser at very high frequency. A transformer is not affected by polarity, since it is an alternating current device, so it matters not to the transformer what the input or output polarity may be. Any polarity on the primary side and any polarity on high tension side will produce the same quality of spark. Why then do we worry about coil polarity? Because the spark plugs do care which way the electrons are flowing in the high tension circuit. The spark plug has a thermally insulated center electrode (surrounded by ceramic). With engine running the center electrode runs substantially hotter than the exposed end electrode. Design of the ceramic insulator determines how hot the center electrode will run, leading to the designation of hotter or colder spark plugs. As electrons go, they love to jump away from a hot surface and fly toward a colder surface, so it is easier to drive them from hot to cold rather than from cold to hot. End result is a difference of 15 to 30 percent in voltage required to make spark "initially" jump the gap on the plug depending on which way it is going. So the spark plug prefers to see a voltage potential that is negative on the center electrode and positive on the end electrode for the very first hop of the spark. Oddly enough, this has nothing to do with polarity of the vehicle electrical system, but it is influenced by the common connection inside the ignition coil. The common knowledge bit about electrons is that they carry a negative charge. For electrical bits (similar to magnetic bits) opposites attract each other and negatives repel. This means the direction of flow of electrons in a car is from the battery negative post through the wiring to the battery positive post (not necessarily intuitive). If you reverse cable connections on the battery the current flows in the opposite direction through the vehicle wiring. For most original functions on the MGA this matters not one whit to anything, as most original equipment in the MGA is not polarity sensitive (except maybe the optional radio). As one end of the primary winding in the ignition coil is connected to one end of the secondary winding, reversing polarity of the coil primary side will reverse the drive direction of the spark current on the output side (even though current in the vehicle low voltage wiring still flows the same way). So reversing vehicle electrical system polarity will reverse direction of spark drive. The engine still runs either way, but spark might be more reliable under marginal conditions if you get it right. The simple fix for this is to reverse the two primary wire connections on the ignition coil. Because the output spark is very much higher voltage (20,000v) than the car battery (12v), it doesn't care if the battery polarity is helping or hindering by a meager 12 to 14 volts in battery potential. So how do we know which way to connect the ignition coil for best results? Original production coils were generally marked on the primary terminals "SW" for Switch and "CB" for Contact Breaker. This was assuming the vehicle wiring was connected for positive earth (positive battery cable grounded on the chassis). If you reverse battery polarity (going to negative earth), then these coils need to be connected with "CB" to the ignition switch and "SW" to the distributor points wire. Later issue ignition coils are marked "+" and "-" on the primary terminals. These are more no-brainers, as you only need to match the terminal markings to the battery posts. For positive ground the "+" terminal goes to the distributor (to be grounded on the engine block). For negative ground the "-" terminal goes to the distributor (to be grounded on the engine block). If you are still skeptical about all this, there is a quick way to check directly which way the current is flowing in the high tension circuit. Disconnect a spark wire from a spark plug (or the coil wire from the distributor cap). Hold this HT wire near a grounding point (or near the connector end of a spark plug), and position the tip of a graphite pencil in between. When you crank the engine (no need to start or run) you can observe the resulting spark jump between wire and pencil, and between pencil and ground (or spark plug). A flare (hard to see) toward the plug (or ground) shows correct polarity while a flare toward the coil shows reversed polarity. If the flare goes toward the coil, just switch the primary wires on the coil and make note of the connections for future reference. Can't see the flare? Not sure yet? You can also check spark polarity using an analog (moving needle) volt meter. Hook up a voltmeter with the negative lead to the plug terminal and the positive lead to the block. Set the meter on the highest volt range. Crank the engine over (no need to start it), and you should see an upward swing of the voltmeter needle (don't be concerned with taking a reading). If the needle swings down off the scale, your coil is hooked up wrong. To correct it reverse coil primary leads. Do not worry about the coil markings, but make note of them for future reference.
Thank you for that^^^! I just got a new coil for my new to me '50 Mercury (6V pos grnd) and the new coil is of course marked +/- and I was unsure of the connection.
Thanks Moose. Still doesn't explain why the factory coil's wired backward from logic and that article. Blem on it's +- markings?? Like I said, the way it's designed it can only be wired like a neg ground car while being on a pos ground car. Anyone else on this particular piece of the puzzle?
Cadillac changed from + to - ground in 1946. If you have a later coil that was installed as a replacement part it could be genuine Cadillac but works the opposite of the 37 original.
now I remember reading somewhere that negative on the coil ALWAYS goes to ground and the positive ALWAYS goes to the ignition switch (regardless of positive or negative ground).
I have an old Farm all Internation tractor and 6 volts and its positive ground.I thinks a pain in the butt every time I have to charge the battery .I have to remember how to hook it up right. Bruce.
I was taught a long time ago the plus side is battery [source] thus add to negative takes away , =points. right or wrong it has always worked fo me. Bruce just hook the charger to the battery as pos and negative just like all of them.
Positive ground = always put positive side of coil to distributor and negative to source. Always. The car will run either way, but it will run better if wired correctly.
On the coil + means the juice , power , voltage whatever you choose to call it gets added to the coil . The points take it away, thus the - . Simple way to keep track
Sorry, but that's not how it works. It's electricity, not plumbing. The reason it doesn't work that way are too complicated to post here, but suffice it to say that polarity matters and you want your spark plug to fire from the center electrode. If your source is (-) then the input to the coil is (-), if your ground is (+) then your distributor is (+).
I agree. But here's the situation. We've been having issues with this 37 Lasalle for a long time. This last time I changed coils I noticed the factory coil can only be wired how what I believe to be wrong. If you look just above the correctly wired generic coil that's now on the car you'll see an anti theft piece just above it. It has the power wire from the ign switch (-) in something similar to a speedo cable housing, and that only can go to the + term on the stock coil. Thoughts?
I work on a few 34 Las for an estate, so that anti theft deal looks familiar. I do have a 34 here, and I can look to see if there is a plus or minus, but I'm not sure if this car still has the correct coil. Lots of stuff was changed in thc 1960s on this 34
i just looked at three original LaSalle coils like that. All three say DIST near the wire going to the points. I also looked to see if there was a plus or minus on the back side; no marks there. Someone on hamb mentioned how to ohms test coils. Maybe they will see the thread
Anti-theft? Like to prevent hotwiring? Can't you just twist the cap off and hotwire? Anyway, I can't explain why the polarity is opposite, except that maybe your coil is a replacement from a later model and not original polarity. You can do the "Pencil Test" and see where the spark comes from on the plugs.
Sorry I do not understand... I've got 6V +ground cars and jumped them from modern 12V -gnd several tens of times. No any problem, no any difficulty there. I'd suppose you don't have 6V tube radio on your forklift? - If you do, disconnect it before jumping the engine, cannot think any other worries. p.s. Would understand if you said you did it for cheaper batteries...
Yeah, I think that pencil test is some kind of hazing practical joke, kind of like a fetching a bucket of steam or a left handed screwdriver.
Does it run OK with that new 2 terminal test coil? ...Unless you can really know for sure if the new "one terminal" coil is marked wrong... Why not figure a way to have the blue wire sneak out of the armored cover cap, and hide that wire behind the coil..... Using the new "normal" 2 terminal 6 volt coil. Nobody would notice or care if the coil was not the right one. It does not look like a high point showcar that would be nitpicked.
It starts and runs better than ever. Like I said, it's had ongoing and overlapping (fix a fuel issue the same time an ign prob would manifest....) problems for a long time. It's getting left alone for now. I told the customer I'm welding the hood shut and putting a 4 foot dipstick thru the side of the hood.
Groucho, I found two old Delco-Remy coils in my "stock" cabinet. Each were marked 538-Z on the side body and one is numbered 1863090 on the metal end cap just like yours. I think 1863090 is the part number for just the metal end cap. They each have "Dist" embossed on the bakelite cap and nothing at the bottom terminal (the top if mounted like yours). One had the anti-theft ring and the other didn't. Yours obviously looks like a later production unit. Delco apparently used the same plastic caps from negative ground coils that were pre-marked (+) and (-) and maybe the production department didn't appreciate the fact that early cars were positive ground, hence they put the terminal on the (+). Yours has the boss for the second terminal, neither of mine has that. The true mystery is how it is wired internally. Only deconstruction or testing can tell you that. Mike
http://www.modifiedcadillac.org/doc...logs/1941 Shop Manual/41 Shop Manual - 71.jpg this wiring diagram for a 1941 positive ground cad sure seems to show the "power" from the switch going to the terminal on the bottom of the coil case. So, is the discrepency that fact the terminal by the high tension lead kind of marked " - " ?. Unless the starting is instantaneous I'd be doing the pencil spark test for sure to determine the stronger spark.
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