Fuel gauge and sender

[Nick Bombini]

Hi guys,

I'm needing a little info on my fuel gauge and sender. The fuel gauge should be a standard gauge used on almost all trucks during ww2, right?

The problem I'm having is the gauge always reads full.

The sender was NOS when installed several years back and the gauge in the truck came in the truck, age unknown. The wiring harness is a new one from Vintage wiring of Maine installed about a year and half ago.

My first thought was there was a short and it was grounding out but there are no shorts between the sender and gauge. From there I decided to try a NOS gauge I have. Same thing, gauge reads full all the time. I have removed the sender and hooked up the nos gauge to it, hooked the gauge to the positive terminal of a battery, the negative to the body of the sender, and moved the float up and down. Same thing, always full.

I have tried three gauges while bench testing the setup, and it always registers full. Now my thoughts are the sender is bad so I checked the resistance with an ohm meter. The sender reads 0 ohms with the float down and 30 ohms with the float up in the full position. As far as I know, these are correct ohm readings for a pre-65 GM vehicles.

Anyone have an idea what the problem is? This is driving me crazy.


--Nick

[Nick Bombini]

Ok, I think I have the problem solved with the help of Bill. I thought that any ww2 fuel gauge would work and I was trying to use a NOS SW for a GPW and the gauge in the truck appears to be for a MB.

I have just learned that jeep sending units use an opposite and wider ohm resistance at 52 ohms empty and 0.5 ohms full compared to GM vehicles at 0.5 ohms empty and 30 ohms full.

That and a ground issue at the gauge were causing all my problems. Now I just have to find a correct GM gauge.

Thanks for the info Bill.

--Nick

[Brad]

wow, I was about to say maybe your fuel tank was full?

[Bill_Wolf]

I sent Nick an off line link to an article originally written 8 years ago by Mike Kelly on the G503 site. I wanted to OK the post here with Mr. Kellys permission before putting the link up here.

Mr Kelly is no where to be found and has left the G503 site without leaving any contact info.

It is an excellent article about HMV fuel gauges. A true bit of knowledge for 65 year old stuff.

So for the benefit of the hobby I will post the article host by me on my server. If anyone knows Mr Kelly please send me his email address off line.

Mr Kelly if you object please contact me and I will remove it

Bill

http://www.cckw.org/pdf/fuel_gauge_problems.pdf

[dr deuce]

If you are doing 12 volts, JC Whitney sells a device that is a bar with a stud on one end and hole on the other with a wire hanging off of it. You just insert the unit onto the gauge using the hole end onto the stud of the gauge and move the feed wire loop to the stud end of the bar. You then attach the extra wire to ground.

BTW: You should also use a 0.01mf capacitor on the input and output of the regulator to ground. Mount it to the terminals on the 7805 or 7806 regulator. This is to prevent the regulator from going into oscillations which they sometimes do. I have used them an many commercial products i have designed and that was always a rule of thumb with them.

[Nick Bombini]

wow, I was about to say maybe your fuel tank was full?

Yeah, I wish! If the tank was always full, I would be in hog heaven. Unfortunately, that's not the case. The truck has an appetite more so now that I tow the USMC trailer to shows.

--Nick