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I have a 1939 110 / six with overdrive. This was my Dad's car and for years he thought the car was stalling due to vapor lock. He rerouted lines, replaced them and finally put in an electric pump. I am now experiencing this stalling, very intermittent and at any outside weather temperaturs. Car will stall, at any speed, including just idling. No misses, just like someone turns the key off. There is not a ballast resistor for the coil, but as I look at the schematic, the overdrive switch, relay and other components are in the 6V path to the coil. I am now suspicious the problem may be within the overdrive circuit. Anyone have similar experiences or suggestions?

For troubleshooting, there should be two wires on the ignition coil primary terminal. One goes to the distributor and the other goes to the OD kickdown sw. Remove the wire going to the kickdown switch and leave the one going to the dist connected. That will totally remove any connection comng from the OD. If the engine still stalls the OD and its circuitry is not the problem however, if the engine runs normally you need to check the OD switches and electrical components for operation and the wiring for bad insulation and possible shorts to ground.

The OD will still engage with the wire disconnected but it will not kick down smoothly (or at all) when passing or when a forced kickdown is requested. Without the wire the ign cutout can not cause the engine to lose torque momentarily and let the OD components disengage. If you find the stalling problem is due to the OD best to repair it or else leave the wire disconnected and lock out the OD until you can fix the problem.

There is an early and late version of the 39 OD wiring. The late version has an extra switch operated by the reverse shift lever at the base of the steering column. If you have that switch, make sure it is only being activated when in reverse.

C'mon Howard...the overdrive is just a ruse. (but excellent diagnostic advice)
Its the ignition switch/cable shorting inside. We've been here before... one bump, and coil is off...

You are right. I keep forgetting about those pesky armored cables since I eliminated mine by adapting a modern switch to the 47 bezel and no longer have the cable. It very well could be the issue. Unfortunately that wire is somewhat harder to troubleshoot unless the coil is the type where the end twists off and terminal is easier to get to.

agreed - but wiring a temporary keyswitch directly to a rockauto coil might be a cheap way to diagnose...
For me, the hidden clue was that the car will die just idling. I'll wager its something in the ignition circuit, switch/cable, or maybe a wire in the distributor?

Dist is a good possibility if it is the type the breaker plate moves. That old fabric insulation will fall off if you give it a hard look and maybe a piece did and wire could be touching ground if the plate moves just right.

Also, if it is the old original coil it could be flaking out too -- although the coil symptom is it usually acts up when hot and is OK when it cools down a bit. Not sure if the time frame between happenings would be good for that possibility.

What about a bad condenser?