Fuel/temp. gauge clarification (again)

Wiring, lights, heater controls, anything electrical..
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martin1953
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Fuel/temp. gauge clarification (again)

Post by martin1953 » Sun Feb 05, 2017 9:45 am

After reading all of the posts regarding the fuel/temp. gauge issues, I am preparing to build a limiter like discussed usuing the (7805 and 7808) limiters with a heat sink for my 64 W300. Should the fuel gauge first receive 12v on the 12v input terminal of the gauge from the 7808 resistor and then connecting the jump wire to the temp. gauage to the 5v output of the 7805 resistor? It appears that 12v need to supply the fuel gauage reducing it down to 5v which in turn jumps over to the temp. gauage giving that gauage 5v.
If the fuel gauage internial step down restistor is burned out, should 5v be fed to the fuel gauage input first rather than 12v? Please clarify once again.

Thank you

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pwadventurer
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Re: Fuel/temp. gauge clarification (again)

Post by pwadventurer » Mon Feb 06, 2017 7:39 pm

I see you have the 300 model, not sure if you have the heavy duty gauges or standard. If you have the standard gauge you can follow the notes in the picture. I have yet to do this modification, but I think I understand the concept. You want to remove the 12 volt feed from the fuel gauge completely and redirect it to bus bar tabs on amp gauge ( also bend bus bar up and away from fuel gauge), and then jumper a wire from tabs to 7808 regulator. The 5 volt feed from the 7805 regulator jumpers with the 5 volt output on the fuel gauge.
IMG_2684 - Copy.JPG
Last edited by pwadventurer on Sun Dec 24, 2017 9:43 am, edited 1 time in total.

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pwadventurer
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Re: Fuel/temp. gauge clarification (again)

Post by pwadventurer » Sun Feb 12, 2017 2:09 pm

IMG_2702 - Copy_edited.jpg
I made the voltage regulator today with a single 7805 device. Input to regulator was 14.5, output 5.06 volts. From different web sites the 7805 has a maximum input of 25 and minimum of 7. This instrument cluster is a spare used for the test.
IMG_2703 - Copy_edited.jpg
Old sending unit , i checked on emty and full.
IMG_2700 - Copy_edited.jpg
Gauge didn't quite reach full but sending unit not in great shape.

after twisting upper stop limit, the gauge read full
IMG_2705 - Copy_edited.jpg
IMG_2706 - Copy_edited.jpg
I added temp gauge on circuit by putting 15 ohm resister (dryer heating element) as sending unit. I checked new voltage regulator for heat 1 hour later and felt very little.
IMG_2723 - Copy_edited.jpg
Last edited by pwadventurer on Sun Dec 24, 2017 9:21 am, edited 4 times in total.

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Hobcobble
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Re: Fuel/temp. gauge clarification (again)

Post by Hobcobble » Tue Feb 14, 2017 11:13 am

:goodpost :goodpost :Thumbsup That's great information.

John

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Re: Fuel/temp. gauge clarification (again)

Post by Randy » Sun Feb 19, 2017 9:03 pm

Thanks for the great pic diagram very helpful now have fuel level, but still no temp had replaced sender going to test it tomorrow and see if that's the problem thanks again. Randy.

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