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Discussion Starter #1
My 404 came with a new fuel gauge in the dash, and a sending unit in a box. I am trying to get them working. Whoever modified the bed seems to have removed the wiring that would have served the sending unit (if it was ever there) There are taped off wires behind the gauge. The sending unit varies the resistance through it as the float moves, all pretty standard. My question is whether anyone knows if the resistance to ground increases as the fuel level increases or vice versa, since I will have to rewire the whole setup. I am not sure which way to set up the float other than by experimentation.
The gauge has a "+" terminal and "g" terminal and one that I assume goes to the sender. There is a rubber plug covering a fourth terminal, no hole for wire passage through it. there are however four taped off wires. I can test voltages to see what carries 24v and what goes to ground, but need to know the orientation of the float, it can go in in a manner that increases ohms as fuel level increases or vice versa. My schematics are more than a little vague on this circuit.
TY
 

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Discussion Starter #2
I'd still like the info, but I managed to break the existing sending unit playing with it by over rotating the contact inside. So If anyone knows the proper setup I'd appreciate the knowledge, but I will be another week or so before a new unit arrives.
 

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I installed a sending unit and gauge some years ago and had to check with a European contact to clarify the wiring. He told me that the "+" terminal is for power, the "G" terminal is connected to the sender [Geber] and the 'upside down 'T" is the ground connection.
My gauge works fine, but it needs some adjustment [for which I am not skilled enough]: full tank is ~ full on the gauge, and empty is ~ half full on the gauge.
I'd be very interested in how you eventually get yours working satisfactorily.
 

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Discussion Starter #4 (Edited)
I installed a sending unit and gauge some years ago and had to check with a European contact to clarify the wiring. He told me that the "+" terminal is for power, the "G" terminal is connected to the sender [Geber] and the 'upside down 'T" is the ground connection.
My gauge works fine, but it needs some adjustment [for which I am not skilled enough]: full tank is ~ full on the gauge, and empty is ~ half full on the gauge.
I'd be very interested in how you eventually get yours working satisfactorily.
I need to learn some german, I'd have hooked that G to ground and never known why it didn't work. As for adjustment that is easy enough, at least on my BMW motorcycle I just had to bend the float arm a little to more accurately read the level. You're just trying to change the relation of the float to the pivot point. Another less seat of the pants approach would be to move the slide on the sender unit to another position. If yours is like mine it has several possible locations for the lower section to mount on the upper rail. I'd guess that moving it up or down (relative to the top of the tank) on that rail would yiel a more accurate reading. I'll post a pic of the one I got and it'll make sense.

So if the red cap is the level of fuel, this would read full, the float is up towards the top of its range.



If you move the position of the pivot, which is where the unit gets its data, it reads half full
 

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Discussion Starter #5
I'd guess that your float arm pivot either needs to be moved lower on that rail, or the float arm needs to be bent into an arc so it turns that pivot farther in its range and tells the gauge that the level of fuel is lower than it is currently reporting. I might be thinking backwards here, but you'll see the logic when you play with it.

If you have an old style toilet, they have a similar float system. pull the tank lid off and play with that float, it'll be easier to get a feel for what happens than pulling it out of your fuel tanks.
 

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Discussion Starter #7
My sender was about 200 Ohms full and Zero when empty. The gauge is quite accurate when still, fluctuates a little when on the road.

Hope this helps



Tony
Thanks. It'll help when the new one arrives. Those values are about what it was giving me. I should have asked first and experimented later, before I broke a contact playing doctor. On closer inspection it makes total sense, since the stops for the arm are shaped in a way that indicates where it should go. I was just in a rush and losing daylight. That blunder will cost me $60 or so.
A further question, is there a cover for the top of the unit? or do the terminals just get painted over?


BK, the values Tony reports should give you an idea of how to adjust your unit also.
 

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Thanks for the suggestions; and, the advice. I did bend my float arm, just a little bit, and slightly adjusted [slid] the arm's position in the attachment at the bottom of the sender; both 'adjustments' to enable conflict-free movement of the float within the tank.
I have no cover for the top plate that bolts to the tank.
I also added a ground wire from the top plate of the sender, to the nearest frame member, simply as a redundancy [?].
When the weather warms up, I will 'play' with it a bit more and try your suggestions.
 

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A further question, is there a cover for the top of the unit? or do the terminals just get painted over?.
Likewise I have no cover plate over the wiring, the terminals are exposed and mine were bare under the dust and dirt. Its worth a thought as with all the crud that gets on top of the tank you'd expect some minor connectivity between sender voltage and earth. By the way, I've read elsewhere about adding an external resistor to correct your fuel gauge reading if the error is linear. Its a common fix for the earliest FI cars when replacement sensors for the FI system are hard to get.

Tony
 

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Discussion Starter #10 (Edited)
Likewise I have no cover plate over the wiring, the terminals are exposed and mine were bare under the dust and dirt. Its worth a thought as with all the crud that gets on top of the tank you'd expect some minor connectivity between sender voltage and earth. By the way, I've read elsewhere about adding an external resistor to correct your fuel gauge reading if the error is linear. Its a common fix for the earliest FI cars when replacement sensors for the FI system are hard to get.

Tony
I can see the simplicity of a small resistor in line, beats pulling the sensor out of the tank. A little research might prove worthwhile.

Project up date: wired in some nice bright off road lights today.. attached to top of bumper just inside the headlamps. Looks pretty good. Pics in the next few days. Next is a bed mounted lamp or rear light of some kind. I have the lamp and switch, just need to run a wire.
 
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