resistor size 1917

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    I have a 1917 Model 38 C4. I am in the process of re wiring the car and noticed that the wiring diagram shows

    a resistor unit located in fuse box #1 position (Plug ignition resistance-45393). First question, does anyone know of a replacement ,

    manual says use a 5 amp fuse but not constantly. My car had a sold copper wire installed. This car also had a resistor mounted on the light switch between the end extension of terminal 2 and the terminal between 5 and 8, not marked. Since the dimmer switch located on the door

    was disconnected, and several wires changed on the light switch that fed the fuse box this may have been a fix for some bad wiring.

    Any help greatly appreciated Thanks.



    John, I looked in three sources and found 3 different answers for the 38 HP car battery ignition(?) circuit resister.

    1) The PAS owner’s manual for C4 is a marked up version of the 1916 model C3. It shows the C3 with a volt meter in the ignition circuit, which will not read properly with a resister. No resister is shown in that diagram, but a pencil note “ammeter?” is in the text.

    2) The PAS Wiring and Tune-up guide, from the Company Store (page 6, for Series 4 &5, 38 & 49 hp), does show a resister and an ammeter. It is a partial diagram, showing no ignition wiring, so no real clue where it fits in the full wiring system.

    3) The PAS owner’s manual for a 38 hp car in 1919 has a wiring diagram with NO connections to space #1, so no resister. The Wiring and Tune-up Guide diagram agrees.

    *If your car has only one battery ignition circuit using a 6 volt coil, and the other a magneto, then no resister is used. *If your car has a volt meter instead of an ammeter, then no resister is used. *If your car has two coils in parallel, then a resister may be useful, depending on effective resistance of the coils – but they should still operate OK for quite a while without a resister. If the coil has a nameplate showing the preferred voltage, then we can do the math for the level of resistance (ohms) and wattage (for heat dissipation) needed.

    My only real experience with a ballast resister was a 1967 Plymouth during college years. That resister was a large ceramic thing that would be difficult to hide on your car. Web references discuss ballast resisters only when using a 6 volt coil in a 12 volt car. My ’29 does not have a ballast resister for either coil. I hope this helps. Best Regards, Herb






    Thanks Herb,

    Thank you for the effort, I may be more confused than before. I have wiring diagram blow ups of the three electrical circuits

    and they seem to correspond to what I have removed from the car.  I do have an amp meter(white face). There is a coil mounted to the firewall and a 7th post on the distributor cap but this appears to be an addition. Perhaps done when the wiring began to deteriorate since most of the fuses were blown and a copper wire was added as a bridge.  It appears the car was used long after the wiring began to fail.

    Thanks again, John


    Hi John, I have recently been dealing with a similar issue, if you give me a call I might be able to shed some light on it…Allen at 217 778 1425


    John & Allen; I may have a fix for your resistor problem. I assume your ignitions are of  the “two battery” type with no magneto. The ignition switch should look similar to the 0ne shown in the 1919 Owner’s Manual, where there is one ignition wire going into the switch and two coming out, one each headed for one of the coils. From what I have seen, most 6 volt coils have a resistance of about 1.2 to 1.5 ohms, using a current of  1.2 to 1.5 amps. Please check the resistance of your existing coils to verify that the primary is about 1.2 to 1.5 ohms. When the coils are in parallel, the effective resistance in that part of the circuit drops to about 0.7 ohms. If the target current of 4 amps is to be met, another source of resistance is needed to reach the total expected value of 1.5 ohms.  For a target of 6 volts and 4 amps to each coil, an additional 0.8 ohms needs to be added to the single wire part of the circuit, BEFORE the ignitions switch. This location puts the resistor in series with the pair of parallel coils. This new resister will generate 25 watts and get HOT.  Do NOT mount it on a wood panel. Use a 10 amp fuse in the block, then hide this resister somewhere under the hood – out of sight, but with plenty of air flow. This is what Chrysler did with most of their cars in the 1960’s.

    There is a resister with 0.8 ohms at Summit Racing. It is from an MSD after-market ignition system. Part Number is: “MSD Ignition 8214” for $13.36 and shows to be in stock. It will keep voltage at each coil close to the nominal 6 volts.  This value may not be exact, but will be better than nothing.  Regards and stay warm, Herb


    Thank you Herb but my car does have a magneto and battery ignition.


    John, With only one 6 volt coil in a 6 volt vehicle, no resister should be needed. Check the resistance of the primary coil, should be between 1.2 and 1.5 0hms. If the coil resistance is below about 1.2, it’s time to look for another coil. The “battery ignition” system should draw about 4 amps, so a 5 amp use should work in your fuse box, but a 10 amp fuse will be more reliable. Check your wire size and condition (new #18 is good for 10 amps, #16 can handle 13 amps. If the wire goes inside a conduit, use #16 – it will take more heat, then use a 10 amp fuse.). I strongly recommend using stranded wire, as solid wire will break from vibration – and that problem is difficult to detect and fix on the side of the road.  Herb


    Thanks again Herb, I am presently re wiring the entire car ,the original wire was in terrible condition this is when I discovered the

    wire soldered to blown fuses. and no resistor.

    Thanks again for your help.


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