1939 Ignition resistor problems

COE Dan

COE Dan

Senior Member
Hello,

I have a '39 Ford with everything stock. I'm having intermittent ignition problems. When the engine is cold, it starts nicely. When hot, the battery is more likely to run down cranking rather than start the engine. In this condition, it appears I get zero spark. I've traced the wiring and being new appears to be connected correctly. What I did discover is that there are 2 ignition resistors mounted on stock fuse panels in the car.

Only one resistor is hooked up, the other is just there. I've checked the resistance and they are different. The one in the circuit is 4.9 ohms; the other is 8.3 ohms. Which one is correct?

Secondly, the battery registers 6.21V at the battery. At the battery side of the ignition resistor, I'm measuring 5.89V. Is this normal voltage loss to the resistor or do I have a voltage drain somewhere upcurrent from the resistor?

Anything will help, Dan
 
Dan,

Allowed voltage drop is .5 volts and just a good cleaning of all connections will more than likely fix that issue.
I would suggest running a jumper wire from the battery directly to the coil
just as a test to see if the engine will start then. If it does you need to do some work on the resistor circuit.
I am assuming its 6 volts right ??
 
Suggest you disconnect battery and put it on a charger due to it's low state of charge. then remove both of the resistors clean all the nuts holding the resistors to the fues block. clean the two terminals of both the resistors. and remeasure I believe 0.5 ohm is approximately correct. Reinstall one resistor and fues block. Then remove the back of the ignition switch and wires, clean the internal contacts and the terminals on the switch. Try it again.
 
Your resister should be .5 ohms not 4.9 maybe wrong reading.
With .5 ohms should read about 1.5 volts across resister.Check it when running don't leave key on for long time when not running.
 
I've seen the old wire wound resistors get cracks in the wire due to constant heat up and cool down. At some point they can get to where they will open the circuit when they get hot then close the circuit after they cool down. Ignition coils can do the same thing so thats why they were always heated before they were tested with the old tester units. Condensers can also get to a point where heat will affect their performance. Many were made with waxed paper back in the day. After the wax gets hot a couple of hundred times, it degrades and rearranges itself to a point where it's capacitive reactance is poor.

Kerby
 
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