ratbailey Posted January 11, 2021 Report Share Posted January 11, 2021 (edited) Hey All, I spent most of yesterday installing some fresh, temporary wiring, just so I can feel confident about starting my '47 DeSoto S-11 without setting fire to it. I'm confused about the depiction of the ignition coil in the schematic (see attached). There's the positive and negative posts, the center connection to the distributor, and then a little dot near the bottom edge of the circle, leading to the "battery" connection on the transmission relay. Where is this damn dot on the coil? Is it the ground connection on the coil bracket? Whoever replaced the coil recently, hooked that wire up to the negative post, but from other things I'm seeing, I don't trust that person. Also, does anyone know if there were deviations from this schematic in S-11s built later in the model year? There's some connections that don't agree with the schematic---I'm going with my regular assumption that someone messed with it, and put things back in the wrong place, but I just want to be sure. Tracing things with an ohmmeter is proving difficult, due to the sheer amount of shorts in the loom. Thanks! -Art Edited January 11, 2021 by ratbailey Quote Link to comment Share on other sites More sharing options...
junkers72 Posted January 11, 2021 Report Share Posted January 11, 2021 (edited) I am in the process of rewiring my 1947 desoto engine compartment also and am confused with the shop manual drawing as well for the coil to transmission solenoid. It makes it appear there is a 3rd terminal but there isn’t. I pulled my falling apart cloth covered wires without tracing prior because I have the shop manual. Edited January 11, 2021 by junkers72 Left out key information Quote Link to comment Share on other sites More sharing options...
Sniper Posted January 11, 2021 Report Share Posted January 11, 2021 Looking at the drawing it appears that third wire is what applies power to the transmission relay. Being that it only should have power with the key in the run position and this being a positive ground setup hooking the wire to the coil negative terminal is appropriate. Having said all that, I don't have this setup so I can't confirm it for you. 1 Quote Link to comment Share on other sites More sharing options...
Loren Posted January 11, 2021 Report Share Posted January 11, 2021 As near as I can tell the wire to the transmission relay (just like an overdrive) is to interrupt the ignition momentarily to take the torque load off the transmission. However, an Overdrive relay is labeled Throttle, Solenoid, Ignition and battery. The drawing you have is labeled differently but it may serve the same function. Overdrives can be wired differently depending on how many wires are on the throttle switch. Four is the standard I've felt with but three is possible. The wire which goes to the coil should connect to the point side of the ignition coil, which is the ground side in order to perform the ignition interrupt function. A positive ground car = positive side of the coil. A negative ground car = negative side of the coil. If the coil is not marked in any way just know if you get it wrong the worst that can happen is a reduction of about 40% of the coil's output. Which means it will still run. Just make sure the relay wire goes to the point side. 1 Quote Link to comment Share on other sites More sharing options...
Sniper Posted January 11, 2021 Report Share Posted January 11, 2021 there is also a throttle interrupt circuit in that drawing, it goes from the PRI terminal on the transmission relay to the coil + and grounds it when it wants to interrupt the circuit. I believe the wire the OP is asking about is nothing more than power to the transmission relay. 1 Quote Link to comment Share on other sites More sharing options...
DonaldSmith Posted January 11, 2021 Report Share Posted January 11, 2021 Confirming the coil wiring for a 47 DeSoto with the semi-automatic transmission. Coil Negative post: (Hot side) Red wire from "coil" post of ignition switch, and green wire to "Bat" terminal of the transmission relay. Coil Positive post: (Positive Ground system) Black wire to "PRI" post of transmission relay, and black wire to distributor. So, the negative post takes power from the ignition switch and provides power to the transmission relay. The positive post takes the timed grounding from the distributor to energize the coil, and the other wire grounds the coil during kickdown, to briefly slow the engine, so the transmission can do its wonders. 1 Quote Link to comment Share on other sites More sharing options...
ratbailey Posted January 11, 2021 Author Report Share Posted January 11, 2021 1 hour ago, junkers72 said: I am in the process of rewiring my 1947 desoto engine compartment also and am confused with the shop manual drawing as well for the coil to transmission solenoid. It makes it appear there is a 3rd terminal but there isn’t. I pulled my falling apart cloth covered wires without tracing prior because I have the shop manual. It's kind of hilarious that someone just 100 miles away is wrestling with the same question, "Where does the battery wire from the transmission solenoid go on a '47 DeSoto?" Quote Link to comment Share on other sites More sharing options...
ratbailey Posted January 11, 2021 Author Report Share Posted January 11, 2021 Thanks, everyone, for the very detailed answers--I would've had to just roll the dice and try stuff, but it's good to have some real answers in order to really know what I'm looking at. This car is quite a fascinating little machine! Quote Link to comment Share on other sites More sharing options...
greg g Posted January 11, 2021 Report Share Posted January 11, 2021 (edited) Thanks for what the trl terminal is for on an OD!!! That has been buzzing in my head for nearly two years. So how do I hook up my hand throttle cable there?? It doesn't want to bend that sharp..... Guess I can reposition the relay! Edited January 11, 2021 by greg g Quote Link to comment Share on other sites More sharing options...
junkers72 Posted January 12, 2021 Report Share Posted January 12, 2021 Thank you ratbailey for posting this issue and also to those who answered. Happy Wiring 1 Quote Link to comment Share on other sites More sharing options...
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