1934 - 1935 Buick A C Gasoline Gauge - Dash unit Series 50-60-90

Would anyone have literature on testing the dash unit. I am interested in check correct resistance on each coil that sort of thing. The literature I have basically says if you have determined that the sending unit is OK and the wiring is OK then the dash unit is bad and should be replaced. I am looking for a dash unit schematic with some test readings of a good unit.

Any Info would be appreciated.

Thx

Ken

Is the dash gauge out of the car or mounted in the dash currently? I have just been thru this recently.

Cheers, Dave

Dave

It is presently out of the car and I have opened the case to see if there were any broken wires or connections

Ken

OK, stand by and I will write up something for you, will see if I can do it tonite.

Cheers, Dave

The attached is a simplified electrical schematic of the fuel level indication system. The gauge part has 2 coils (AB and BC in the dwg) of approximately equal resistance. A potentiometer in the fuel tank, attached to a float, is in parallel with the BC coil, with the pot wiper connected to ground and one end of the pot resistance connected to the junction of the 2 coils in the gauge.

Since you have the gauge out of the car checking it is pretty easy. You want to ensure that the 2 coils have continuity first. Get a good ohmeter and first check between the 2 terminals on the back of the gauge - this tests coil AB. IIRC it should be in the neighborhood of 100 ohms but I could be mistaken, mine is back in the car so cannot check now. Check coil BC by going from the tank sending unit wire connection (the one connected to a wire going to the rear of the car, on mine it's the left terminal looking at the back of the gauge case) to the gauge case. This reading should be in the same range as coil AB IIRC.

Since the tank wire is disconnected check the resistance of that wire to ground. The max resistance of the tank sending unit pot is in the 20 ohm range so you should get between near 0 to 20 ohms depending on tank fuel level. If you bounce on the rear of the car while watching the meter is should vary some - this is due to float movement and will give you a sanity check on the tank unit.

If the gauge checks out you can cobble up an emulator on the bench. Get a 6V battery or a 4 D cell tray at Radio Shack and some clip leads. Also get some low value resistors like in the 1 to 5 ohm range.Hook the neg term of the battery to the gauge case, hook the pos term to the 6V connection of the gauge (not the sending unit connection). With nothing connected to the other terminal, the needle should peg. Now clip the sending unit connection on the gauge to the gauge case and the needle should go to empty. Lastly, put about 5 to 8 ohms of resistance in between the sending unit connx and the case you should get a midrange reading of the needle. If you can find a low value pot (in the 1k or less range) then hook that up in place of the individual resistors and you can vary it and see what sending unit resistances are required for 1/4, 1/2, and 3/4 tank readings.

Cheers, Dave

Thank You for the Information Dave

Ken

Thanks Dave. That is the clearest explaination I ever read about checking one. I might even be able to do that!