Coil resistor for stock 37

mark180

mark180

Member
I got a new remote coil for my 37 from Joe’s. It mentions using a different ignition resistor. I think it is located on the inside of the firewall, but I’m not sure. What does the original look like? My car is all stock except for being changed over to 12 volt.
 
Look at the resistor on the inside of the firewall to the left and above the steering column. There will be a caged circuit breaker box and a resistor below that. it will look like wire wrapped around a ceramic cylinder. In the stock 6 volt car there would be a wire from the ignition switch to one end (the right end) of that resistor. The wire from the other end goes to the battery side of the coil, because the stock coil wants about 4.2 volts instead of 6. When the points close and current is flowing through the coil, that resistor drops the voltage at the coil.



Most 12 volt coils have an internal resistor and do not require that resistor to drop the voltage. When the conversion to 12v was made, the wire that originally went to the coil would have been moved to the same end of the resistor as the wire from the ignition switch, effectively bypassing the resistor and sending the full 12 volts to the coil.



If you find that the resistor under the dash has been bypassed, you need to verify that the new coil does not require a separate resistor. What do the instructions with the coil actually say?
 
In a 12 volt system with points, a resistor is usually required. While some cars had coils with an internal resistor, some did not. 12 volt Fords had a separate resistor which was used for a number of years. In the 60's, Ford went to a resistor wire rather than a separate resistor .

Coils with an internal resistor are still available.

Usually, an electronic ignition uses a full 12 volts so a resistor is not required.
 
Last edited:
drolston said:
Look at the resistor on the inside of the firewall to the left and above the steering column. There will be a caged circuit breaker box and a resistor below that….QUOTE]

The OP stated that his 1937 Ford was all stock but for the conversion to 12 volts. There was no circuit breaker in a 1937 Ford. The Ford’s lighting circuits were protected by a fuse until 1940, when the fuse was replaced with what has been described as a circuit breaker, which in fact provided a momentary interruption of the circuit before resetting, in practice allows headlights to shine dimly so the driver can safely limp home in the dark. The rapid action of this unit results in an audible sound of buzzing.
Click to expand...
 
www.joesantiqueauto.com/igntion-coil-b-12000-12v

A 12 volt ignition circuit needs about 3 ohm total resistance to limit the current running thru the coil and points. Joe's "12 volt" coil is 1.5 ohm, perfect for a 6 volt system. To run on 12 volt it needs an external resistor to provide another 1.5 ohm. You will need to use the resistor noted in Joe's product description. (The original Ford resistor is only about 0.4 ohm, so it won't work)

OR... just get a 3 ohm coil, something like the Bosche Blue. No resistor required.
 
Last edited:
You must log in or register to reply here.
Back
Top