Dimmer coil

[ch1929]

The dimmer coil is missing from the back of my ignition switch. What size wire is it and how many coils does it have? 23 Dodge Coupe

Thanks,

Roland

[Pete K.]

Here's a photo of the back of an early Dodge switch. The dimmer coil is insulated wire, dual coiled, measures 3 Ohms. I would just replace it with a carbon type resistor, 3 Ohms, Wattage I'm not sure of, maybe 10 or 20 Watts??

[ch1929]

Thanks Pete, I will give that a try.

[Pete K.]

Roland, About the Wattage of the replacement resistor,"size does matter". The smaller the physical size of the resistor, the less Wattage it will carry without burning up. One would need to know the Wattage of that system, being the high beam headlights, stop and tail lights, wiring, to and from, and the connections, and an extra safety margin. This I don't know, as I don't have a Watt meter, like the type "Fluke" used to make. (I think they still do). I'm very surprised no one else has commented on this thread, since many of those coils are either missing or damaged. I do know in this state, one does need to have working lights for the inspection sticker, even with antique auto plates, or "year of manufacture" plates. I personally want my lights working correctly anyway. Without the dimmer coil, do the lights work anyway? I imagine one could not dim the high beams?

[TonyAus]

The dimmer only operates on the headlights. The correct headlight bulbs are 21cp (50 watts) each. Therefore a three ohm resistance rated to carry more than 100 watts would suffice.

[Pete K.]

Thank you Tony!---Pete.

[ply33]

The dimmer only operates on the headlights. The correct headlight bulbs are 21cp (50 watts) each. Therefore a three ohm resistance rated to carry more than 100 watts would suffice.

The old GE lamp guide I have shows typical 21cp filaments as 6.4v and 2.63 amps which works out to 16.8 watts. Call it 17 watts for one bulb and 34 watts for two. At rated voltage and amperage, those 21cp filaments will be presenting 2.4 ohms resistance with two wired in parallel showing 1.2 ohms to the electrical system.

Adding a 3 ohm dimming resistor to that circuit would result in a total resistance of 4.2 ohms which at 6.4 volts should draw 1.5 amps. 1.5 amps across your 3 ohm resistor will be 6.7 watts.

I've probably messed up the arithmetic somewhere, but it seems a 100 watt rating on the resistor is very conservative. It also seems that the head lights will be very dim with 3 ohms in series with them.

[TonyAus]

Small problem with your calculation. The Dodge uses 12 volt bulbs. However, I can say that the dimming arrangements on my car work well with 50 watt bulbs and the original three ohm resistance coil.

[ply33]

Small problem with your calculation. The Dodge uses 12 volt bulbs. However, I can say that the dimming arrangements on my car work well with 50 watt bulbs and the original three ohm resistance coil.

So it uses something like a 1141 bulb, a S-8 bulb with single contact bayonet base rated at 21 cp at 12.8v and 1.44 amps?

Bulb resistance would then be 8.9 ohms. Two in parallel would be about 4.5 ohms. With a 3 ohm dimming resistor the circuit would be 7.5 ohms drawing 1.7 amps. Call it 2 amps. Across a 3 ohm resistor that would be 12 watts. Again, a 100 watt dimming resistor would be overkill.

But I can see that the dimming effect would be a lot less than it would be on a 6v system.

[platt-deutsch]

Hows about hooking about 8 5amp diodes in series. They would drop about .5 volts each..

[ch1929]

Thanks to everyone for the information. I will let you know how it works out.

Roland

[Guest Doobby]

Anyone know where I can find a switch for my '27 Coupe? Not even sure what I'm looking for.

[ch1929]

Thanks to Myers, I was able to get an original dimmer coil. I now have headlights!!!!!!!!

Roland

[Guest occrj]

As there's a thread running, I'm curious to know just how "dim" the lamps on dim setting should be? My headlights work well, on "dim" however the bulbs are only emitting a faint orange glow - does that sound correct? As far as I know the wiring and switch (12v) are original, with the rear-mounted dimmer coil on the switch.

thanks, Richard

[platt-deutsch]

The original bulbs were 21 Candle power. If you put 32 CP lamps in it they will draw 1/3 more current and thus drop the voltage much more than if the 21 CP lamps are used. That may be your problem.