Dead fuel gauge but voltage reg ok

[Dster]

Help!! Redoing a 69 2000 (slowly only a newbie can do!!)
My fuel gauge is dead so I took it off. I replaced it with a buck reducer that outputs 9 volts to a 12 volt input. However it still doesn’t work. When I check the input voltage from the black wire, it’s 9 volts - isn’t it supposed to be 12v? I can’t tell where the input from the gas tank comes into the picture. Just for the heck of it, I tried connecting the 9 v black wire up to the yellow and black wire-nothing! I think I’m missing some fundsmental issue here, for example, maybe the power line in has to be accompanied by an input from the gas tank itself? I don’t see this in the schematics? If this is the case, maybe that’s the line that’s bad?
Any idea would be sorely appreciated!

[ppeters914]

1. Did the fuel gauge ever work?

2. If the fuel gauge is out on your bench, does it peg to Full if you briefly put 12V to the leads?

3. You say voltage regulator is okay. You're referring to the instrument voltage regulator, correct? Does that mean the water temp gauge works?

[jrusso07]

Have you checked the sending unit in the gas tank? Here is a post that might help: viewtopic.php?t=23210

Here's a schematic from Curtis that shows the power source to the sending unit in the tank. It's a two contact L-shaped connector located under the main harness under the clutch master cylinder...https://kendo-usa.org/datsun/datsun_par ... _69_70.pdf. See the yellow wire from the "To Gas Gauge".

[Dster]

The fuel gauge hasn’t worked in a year. The temp gauge also has no reading. I took the instrument voltage regulator out and put in a buck reducer at 9.4 volts and still no fuel gauge or temp movement. I sanded off the contacts on the sender unit. I also tried running a line from the sending unit directly to the proper plug in spot with nine volts going to the corresponding power inlet also.
I’ve never taken out the whole gauge unit from the dash but tried just taking out the VR and letting 12-14 volts go right through and still nothing on the fuel gauge. I’m reluctant to believe it’s the fuel gauge itself as the temp gauge is also not working. I took out the sending unit and the ohms were indeed variable. I’m stumped!

[davdav2000]

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[davdav2000]

Help!! Redoing a 69 2000 (slowly only a newbie can do!!)
My fuel gauge is dead so I took it off. I replaced it with a buck reducer that outputs 9 volts to a 12 volt input. However it still doesn’t work. When I check the input voltage from the black wire, it’s 9 volts - isn’t it supposed to be 12v? I can’t tell where the input from the gas tank comes into the picture. Just for the heck of it, I tried connecting the 9 v black wire up to the yellow and black wire-nothing! I think I’m missing some fundsmental issue here, for example, maybe the power line in has to be accompanied by an input from the gas tank itself? I don’t see this in the schematics? If this is the case, maybe that’s the line that’s bad?
Any idea would be sorely appreciated!

When you say you removed your fuel gauge and replaced it with a buck reducer, do you mean that you removed the actual gauge cluster or do you mean you removed the voltage reducer that mounts under the steering wheel and provides power to both the temp gauge and fuel gauge? If you haven't checked that voltage reducer, that could be your issue.

[Dster]

It’s the voltage regulator that I removed. I tried replacing it with a variable digital unit that puts out a constant 9 volts. Then I tried just connecting the two voltage regulator leads to each other, which provided about 12 v to the fuel gauge- no gauge movement.
I’m going to hook up the 9 volt supply again and run the engine to see if the temp gauge moves. I wonder what the chances are that BOTH the temp and fuel sensor wires are bad? I’m not sure if they run close to each other anywhere as one is from the front and the other is from the back …

[ppeters914]

Have you checked the sending unit in the gas tank? Here is a post that might help: viewtopic.php?t=23210

Here's a schematic from Curtis that shows the power source to the sending unit in the tank. It's a two contact L-shaped connector located under the main harness under the clutch master cylinder...https://kendo-usa.org/datsun/datsun_par ... _69_70.pdf. See the yellow wire from the "To Gas Gauge".

Here's a complete, working link:

69-70 Gauge Layout
https://kendo-usa.org/datsun/datsun_gau ... _69_70.pdf

Whenever both the water temp and fuel gauges aren't working, the most likely culprit and first thing to check is the gauge voltage regulator. I had to Google what a buck reducer is. I have no idea if that option will work on the stock gauges.

Usually, grounding the positive lead (Yellow wire) on the fuel sender should cause the fuel gauge to go to Full, which would confirm that the fuel gauge is good. Ignition needs to be on, but the engine doesn't need to be running.

[Dster]

This helps immensely! Thanks!

[Dster]

Ok I figured it out with lots of help and hours! In retrospect I think just really cleaning off the terminals of the sending unit was the most important part…that and having enough gas in the tank to register on the gauge!…