'49 car fuel sending unit testing
 

Any way to do it? I'm putting a mustang tank in and I'm thinking about modifying/using my original sender so I can use the factory gauge (no, it's not a 70/10 ohm gauge). All the gauges are disconnected and the wire at the sending unit was corroded and looked to be torn off the sender so I have no idea if it works or not

Re: '49 car fuel sending unit testing
 

First, find out if the sending unit works. Remove it from the tank and place it on a piece of cardboard. Then run a wire from the gauge to the top of the sending unit and a separate wire from the metal flange on the sending unit to ground. Then turn on the ignition switch and manually move the float thru its range of motion to see if it registers on the gauge.
Check the float to make sure it has no hairline cracks. Cracks are common in old sending units.
Also read all the info. relating to gas tank sending units listed here:
https://www.fordbarn.com/forum/searc...rchid=25832191

Re: '49 car fuel sending unit testing
 

Thanks for the response. The problem is I have no 6v battery. I'm in the process of rewiring and switching the car over to 12v. I don't want to spend money on a voltage reducer for the gauge just to find out the sending unit is no good and then have to buy an aftermarket gauge anyway. I was hoping there was a way to bench test it

Re: '49 car fuel sending unit testing
 

Go to Home Depot or Lowes and buy a 6V dry cell. See first photo. Here's some info. about 49-51 Merc sending unit that also applies to other King Sealy units and gauges. The gauge and unit shown here is for a 1940 Ford. It operates same as a 1949 Ford.

Re: '49 car fuel sending unit testing
 

Doesn't a 6 volt dry cell cost about as much as a voltage drop unit these days?

I quit buying 'em years ago because of the cost.

Re: '49 car fuel sending unit testing
 

Do you mean a lantern type battery? I suppose that could be 9 bucks well spent

Re: '49 car fuel sending unit testing
 

Lantern batteries are a standard part of my 6V troubleshooting kit. Great for light sockets and horns and having for long road trips when I expect issues. Rewiring my '35 was made easier with this temporary source.

Powering up a fuel gauge and sender would be easy, but last time I did it for a '36 years ago was with a wet-cell 6V. Gauge is in the box and sender in the vise.

https://www.fordbarn.com/forum/attac...6&d=1356889180

Re: '49 car fuel sending unit testing
 

I always took the wire off the sending unit and grounded it. Turn the ignition on and if the fuel gauge goes up to full then the problem is the sending unit. If the fuel gauge doesn't move the problem is usually in the gauge.

Re: '49 car fuel sending unit testing
 

The wire to the sending unit was frayed, torn away and tied to the frame. The two times we started the car prior to me buying it, we used a gas can since the tank was in horrible shape and the gas was waaaaay past bad. He had one of those three gauge kits under the dash which all worked but none of the stock gauges moved. I'm going to try the lantern battery and use a jumper wire from it to the gauge. I was mistaken in that all the gauges are hooked up behind the dash but I dont want to rip wires off just yet. I'm putting a new harness in the car so I want to keep it as is for reference as I go

Re: '49 car fuel sending unit testing
 

For a six volt source I use my old battery charger. Has 6 and 12. And as for the cracked float I use a cork from a 'magnum' wine bottle. My son has a wine shop so he saves them for me. Same dimensions, and I usually coat with epoxy.

Re: '49 car fuel sending unit testing
 

CJ: Take plenty of BEFORE and AFTER photos of the wiring behind your dash and instrument cluster so as to put your mind at ease and make it easier to reassemble.

Re: '49 car fuel sending unit testing
 

So I just tried testing it. Got the 6v dry battery, made a jumper from the positive battery post to the gauge power post, a jumper from the sending unit center screw to the sending unit input on the gauge, a ground jumper from the sending unit bolt flange to the negative battery terminal and from a ground on the dash to the negative battery terminal. Heres what I saw...it didn't do shit haha. I tried it on the temp gauge and it was the same thing. Either the ground on the dash wasn't good (I tried it in a random hole on the bottom and holding the wire against the gauge cluster housing itself) or the gauges are fired. I'm thinking someone hooked up 12v to the car at some point, maybe to jump it or to charge the battery or something. Now I'm not sure what to do. Anyone have a known good cluster they want to sell?

Re: '49 car fuel sending unit testing
 

Or I suppose it could be the sender is bad. If someone has a known working one I'm definitely interested

Re: '49 car fuel sending unit testing
 

I'm going to ground out the fuel gauge to see if it moves, which I didn't think about last night so we'll see what happens

Re: '49 car fuel sending unit testing
 

Here's the dry cell hook up. This was done with gauge cluster removed from dash but, you could do the same using your dry cell BUT, FIRST DISCONNECT YOUR CAR BATTERY as the dry cell is now your power source..

Re: '49 car fuel sending unit testing
 

I tried grounding out the sending unit on both the temp and fuel gauge and neither one did anything at all. I hooked the power input from the gauge to batt positive, I grounded the gauge housing to batt negative and the sender input to batt negative

Re: '49 car fuel sending unit testing
 

Did you hook up you wiring as shown in the pictorial sketch above?

Re: '49 car fuel sending unit testing
 

I did but I must be doing something wrong. I did it exactly in the picture as shown and I also ran a groundwire from the gauge to the negative terminal on the battery. Stll nothing on the existing gauge. I also tried grounding the sending unit wire on the negative battery terminal and nothing.I ended up buying an NOS set of gauges. I got the fuel gauge today and tried to test it and it's not moving either. I know this is a good gauge since it's NOS and it's never been installed so I'm not sure where I'm going wrong.

Re: '49 car fuel sending unit testing
 

Disconnect you battery so that only the dry cell power is feeding your gauge.
Connect the wire from the + terminal of your dry cell to the correct (input) terminal on your gauge.
Then connect a wire from the other gauge terminal to the screw on the top of your sending unit.
Then connect another wire from the negative terminal of your dry cell to the metal flange where the screw holes are on the gas tank sending unit.
Make sure all the connections are made on clean metal and make sure that your sending unit is resting on a piece of insulation material like a piece of cardboard.
When you do this your gauge should work.

Electricity is not my strong point but, I think you should make sure your gauge is isolated and not grounded to your battery. Use only the wiring shown in the sketch.

Perhaps another Fordbarner will chime in.

Re: '49 car fuel sending unit testing
 

I dont have the battery in the car at all. I did the in car test with the sending unit in my hand. When I tested the nos gauge I got today I did it on the kitchen counter. Should I try with everything saying on cardboard? I also tried the new gauge with the 12v mustang tank sending unit. That was through the 6v battery though so I not sure how well that would work...it also didn't move the gauge