Gas tank sender unit

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    Hi Again. Re my previous enquiry. I have since discovered what the unit REALLY is! A Motormeter Nagel Type Model RKD. Mine is definitely RKD’ed!! Really Knocked Down! everything except the housing that that screws to the tank has long since gone to that Great Gas Tank in the Sky! I have sourced a Cadillac one which is similar which I can rebuild. HOWEVER

    I need to know the ohm value of the resistor that goes between the gauge & the Ign Switch.

    As always the info on the system was in the PASB’s. BUT NOT anything about the resistor value. Not that I can find as yet. Cheers—jak.



    The Nagel unit as used on the 1928 pierce has a resistor value of 120 ohms that is the wire wound potentiometer that is c shaped and fits in the housing. It is wound with .008 resistance wire. The moto-meter brand shows an external resister but the w.c. Nagel unit does not show one in the pierce parts break down for the 1928 Pierce Arrow. The sending units look alike both internally and externally.These type units were used on several cars 1927 and 28 chevy comes to mind and there were others but can’t remember which ones now. I don’t know what the difference is to require an external resistor for the motometer unit. I know this doesn’t answer your question but it is a little more info.

    Regards, Joe


    Thank you Joe

    VERY helpful info. Someone here ALWAYS knows the answer! Now for the external resistor. The original Nagel literature says (and I quote) “A lead from the No. 1 terminal of the dash unit is connected to the ignition terminal of the switch or directly to the ammeter through a special resistance unit. It is important that this resistance be wired in the circuit.”” The Motormeter Nagel Type unit is shown on the 1929 parts book wiring diagram. This is what my car has.

    Again many thanks Joe. Cheers



    Further to the above —here is a wiring diagram of the unit. As all members new to uploading a photo say “I hope this works!””-Jak.”



    The picture look like the moto-meter the only visible difference that I can see is the design of the wiper that contacts the wire wound resister. Pierce must have changed mfg. in 1929. I have a friend that has a book that covers the 1920 auto and will ask him to see if it shows the resister, value, if it does I will send it along.



    Well I guess if you keep referring to our PASB’s long enough you will find the answer to virtually everything about Pierce Arrows. PLUS along the way you learn lot of things you didn’t know! The answer to my resistor question is 300 ohms. It was in PASB 71-6 page 4. Magic stuff & worth a read. I should have spent some time researching instead of lazily asking up front!! Jak.


    Is it possible to use a universal sending unit and a different fuel gauge so that we dont run out of fuel? I have a 34 840A Sedan and have been going off the mileage meter to fuel up after 100 miles down the road on a full tank.


    Good day Richard, As long as they are the same rated voltage as your car I suspect it would work. Is your system 6volt Nagel? The resistor in the original 1929 Nagel system was 300 ohms. Dave Murray supplied me with an original tank sender unit allowing me to restore the original system. I obtained a resistor from the the Aussie equivanent of radio Shack. About 6 to 8 months ago there was someone selling on eBay new sender units of the correct type for 1929/30 cars. WHO??? you ask

    ????? Do not remember!! Good luck with towing a gasoline tanker behind your 34 car!!!!


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