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  #1  
Old 08-03-2005, 12:02 AM
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Fuel Gauge Wire Resistance

I just finished hooking up a new fuel gauge sender and I am getting no reading at the gauge. The resistance at the sender is 47 ohms and I have just over half a tank (just what I would expect with a 0 - 90 ohm sender). However when I read the resistance at the gauge in the dash I am getting 99 ohms. This is being read as an empty tank by the gauge, as it is more than the 90 ohm rating of the gauge.

Does anyone have any idea what might be going on here? Is it possible to have 50 ohms of resistance in the 20 feet or so of wire between the gauge and the sender?

Any help would be greatly appreciated.

Thanks,
Mark

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  #2  
Old 08-03-2005, 08:46 AM
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Quote:
Originally Posted by skydvrboy
...Is it possible to have 50 ohms of resistance in the 20 feet or so of wire between the gauge and the sender?
Not really, but a loose or corroded connector can add resistance.

Check the connectors for corrosion. Also check any connections from sender and/or gauge to ground.

Best Regards,
Jim
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  #3  
Old 08-03-2005, 09:09 AM
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Question

WHAT year & model?????
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  #4  
Old 08-03-2005, 09:29 AM
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All of the connections and wires are brand new, but that doesn't mean they are tight so I will check that tonight. My Mercedes is a 92 300D, which is a 124 chasis, but this fuel gauge and sendor came from another MB, year and model unknown.

The part that is really confusing me is that I measured from the bare wire near the tank to ground and got 47 ohms and then from the bare wire near the gauge to the ground wire and got 99 ohms. I would think this would isolate the problem to the wire.
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  #5  
Old 08-03-2005, 09:33 AM
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Exclamation

AT the cluster measure the resistance between pins 1(ground) & 3 (guage signal), you should have the same resistance that you have at the sensor!
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Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
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190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
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  #6  
Old 08-03-2005, 10:47 AM
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That is exactly what I am measuring, the resistance between pins 1(ground) & 3 (guage signal), but I am not getting the same resistance as at the sender. Any ideas why?
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  #7  
Old 08-03-2005, 11:35 AM
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Quote:
Originally Posted by skydvrboy
That is exactly what I am measuring, the resistance between pins 1(ground) & 3 (guage signal), but I am not getting the same resistance as at the sender. Any ideas why?
Quote:
Originally Posted by Jim H
Not really, but a loose or corroded connector can add resistance.

Check the connectors for corrosion. Also check any connections from sender and/or gauge to ground.

Best Regards,
Jim
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  #8  
Old 08-04-2005, 11:55 AM
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Well, I now have the same resistance at the gauge as at the tank. I determined that there was additional resistance in the brown wire that I had tapped into as a ground. I ran a new ground wire directly from pin 1 to a bolt above the gas pedal and the resistance is the same.

This didn't fix my gauge problem however. I think that the circuit board on the back is broken and I'm losing continuity. Does anyone know if the fuel gauge and temperature gauges will work without the circuit board on the back?

I have installed this in the right side of my instrument cluster where the tach and clock used to be. I am using this to monitor a second tank and the temperature of my heated fuel, so I don't need all the other stuff on the circuit board (warning indicators, blinkers, etc.). Those are all run by the original circuit board behind the original fuel gauge, temp gauge, etc. on the left siide of the instrument cluster. What I need to know is, can I pull the gauges off the circuit board and wire directly to them?

Thanks,
Mark

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