gauge and sending unit questions

[Twiggyb2]

I'm helping my friend with a 1950 dodge B2B. The truck has been converted to 12 volt and the fuel gauge dose not work. I looked under the truck and it seem like the sending unit is hooked up with no resistor. is there a way to check the sending unit with out puling the tank to see if it works? If it works how do I check the fuel gauge to see if that works? I know that a new sending unit cost around $80 and my friend dose not want to spend that unless absolutely necessary and is not good with electric systems at all. That is why I'm inquiring about this.

Thanks in advance for any and all help.

[Jim Shepard]

There is an access plug under the seat. No need to pull tank.

[Twiggyb2]

is there a way to test the sending unit is or is not fried (because it may have been hooked up 12volt with no resistor) and to get the gauge to work do i put a resistor on the send unit wire and on the gauge wire or just to the sending unit?

thanks

[Merle Coggins]

The sender is just a variable resistor. Pull out the lower seat cushion and find the plug in the floor that would be above the sender. Once you get the plug out you can access the top of the sender. First, with the key on try grounding out the wire terminal. If the gauge pegs to full when the wire is grounded than you know that the wire and gauge are working. You can test the sensor by checking the resistance between the wire terminal (wire disconnected0 and ground. As I recall it ranges between 10 and 90 ohms depending on how full the tank is. Often times the issue is that the sender body isn't grounding to the chassis because of rust/corrosion between it and the tank, or on the tank mounts. I added a ground terminal to my sender and added another wire to the chassis to ensure a proper ground for the sender.

As for your resistor theory... If you add a resistor between the gauge and sender it will alter the level readings. You would need to add a resistor in the power supply wire to the gauge to drop the supply voltage back to near 6 volts at the gauge.

Merle

[HanksB3B]

Merle,

I think somewhere you had posted pictures of your added to your sender and another wire to the chassis. I would really help me to know exactly what to do.

Although I have a JC Penny unit in a box, before I drop my tank, I'd like to be sure the problem is not just poor grounding.

My tank was powder coated and I suspect I never sanded the paint where the gauge mounts and maybe the paint on tank itself and its mounting points have a no-ground condition.

Thanks,

Hank

Edited March 28, 2012 by HanksB3B

[Merle Coggins]

This picture? I just found some free space in the flange and drilled a hole, inserted a machine screw with a nut and a little sealant. This new "stud" has a ground wire attached.

[HanksB3B]

Thanks Merle,

Nothing beats doing it right the first time.

Hank

[Twiggyb2]

Thanks Merle,

Nothing beats doing it right the first time.

Hank

Agreed!!! thanks for all you help.

[pflaming]

What a timely post. I am finalizing the wireing now that I have good gauges and the fuel gauge was on my mind. I wasn't aware that those imprints in the floor were 'access' covers. THANK YOU! The forum is my truck salvation. Thank you to twiggyb, Hank, Jim, and Merle. OT: I shot some PB Blaster, then a blast of air, then electrical cleaner into my 'stubborn' panel switch. Now it doesn't work. Took me all morning to find out it wasn't working!!!!!!

Edited April 5, 2012 by pflaming

[B1B Keven]

What a timely post. I am finalizing the wireing now that I have good gauges and the fuel gauge was on my mind. I wasn't aware that those imprints in the floor were 'access' covers. THANK YOU! The forum is my truck salvation. Thank you to twiggyb, Hank, Jim, and Merle. OT: I shot some PB Blaster, then a blast of air, then electrical cleaner into my 'stubborn' panel switch. Now it doesn't work. Took me all morning to find out it wasn't working!!!!!!

Send me the panel switch with the other 'goodies'. I'm gettin' pretty good at fixing those also.

[pflaming]

Yep, right where you said it was. That saved me a LOT of time. I thought the tank was coming out and working on the floor, that is not a fun task. So important to read posts and watch for the things in the background or between the lines. Thanks guys!

Edited November 4, 2017 by pflaming

[Jeff Balazs]

Hey Paul;

I don't know if you have already dropped the tank and cleaned it.....but if you have not I would guess that you should. I was thinking that mine wouldn't be bad......boy am I glad I did this. What a mess! Lot's of crap inside.....and I had to have several pinholes repaired and have it lined. You sure wouldn't want to put gas in it if it was any where near as bad as mine was.

Jeff

[pflaming]

I have had mine off. I got lucky again, with a very good flashlight and a friend with an eagle eye for detail we looked inside. It was all shiny, like glass. There were a few pinholes on the front top shoulder which I sealed, so I'm good to go, but thanks for the concern. I even removed the sender and checked it. I did NOT replace the cork, maybe I should do that now or at least remove it and see if it floats. Or attach one of the Excedrin bottles that are littering my shop.

Edited April 5, 2012 by pflaming

[Watash]

Thanks for all the info.  I just installed a new sender and the gauge went from completely empty (not moving at all) to completely full (still not moving at all).  I am thinking the wire from the tank to the gauge must be grounded.  That's my next project.