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My gas gauge on my '54 6100 12 volt conversion is not working. It always registers 1/2 a tank. At first, it was the float as it had a hole in it. I thought that I had that fixed but now it registers empty all the time. I decided to change out the send unit. It still says empty. Does the attached photo look correct on the sending unit? If so, it's on to getting a new gas gauge.

Sounds like you have a mismatch between the gauge and sender. The '54 should have a 0-30 ohm system, 0 ohms at empty, 30 ohms at full. If this is good, the gauge may be bad.

How can I check that properly?

It looks like your resister may be mounted in the wrong place. My resister is mounted on the positive lead going to the gauge from the ignition switch, cutting the voltage so the gauge doesn’t see 12 volts. Your picture shows a resister mounted on the wire going from the gauge to the sending unit so your gauge see 12 volts then gets cut down to protect the sending unit. You may have burnt out the original 6 volt gauge so that may be why it is not registering.

Can you post a photo of yours so I can see how it should look?

Yes, your runtz is in the wrong place. Read this:
https://fifthaveinternetgarage.blogspot.com/2015/11/the-runtz-story_10.html

At the sending unit, after removing the runtz ("resistor") you should have two wires. Connect the brown wire that goes to the gauge to the center post. Attach the ground wire (white wire that runs to body) to one of the sender mounting screws.

I'll try that out tomorrow, Thanks.

How does one remove the gauge from the dash?

You shouldn't have to take the gauge out. Pop the seat out to give yourself more room to work. I put a plank down to lie on while under the dash. Disconnect the hot wire from the gauge and install the runtz. The hot wire attaches to the other end of the runtz. The black wire that comes out of the runtz connects to ground - probably can connect it to one of the screws that holds the cluster to the dash.

I believe that I need to replace the gauge itself as well. It seems to be totally dead.

First thing I would do is test to confirm gauge is fried:
https://www.fillingstation.com/articles/fuelgaugetesting.htm

Removing cluster has been discussed on this forum before (e.g.):
https://www.stovebolt.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=1008359

If you do have to replace the gauge, you can buy a 12 volt version so you won’t have to mess with a Runtz (resistor) anymore. I just ordered one from Classic Parts. This one is for a 54’.

https://www.classicparts.com/1954-55-1st-Fuel-Gauge-12-Volt/productinfo/24%2D725B/

I went through this drama a few years ago, including installing a Runtz that worked very well; until a few years later after the introduction of alcohol in the gas. I thought the Runtz had failed. By this time 12V gas gauges were available for 47-53 trucks so I installed one. The gauge still read low - never over 1/2 tank. So I bought a sending unit and installed it. Gauge never moved at all after that - stayed at 3/4 no matter what. So I took the sender out and examined it closely. I discovered that the hole pattern on the sender caused the float to jam against the side of the tank. So I got out the old sender and looked at it carefully, measured the ohms, yep 30 ohms like its supposed to be. Hmmm, the cork float seems heavier that I would expect. Put the cork in a can of gas and watched it sink toward the bottom.

So I put the old sender back in with the brass float off the new sender in place of the cork one. Gage has read correctly ever since. After the cork float had dried out it floats once again but it'll stay in the parts box with the new mis-drilled sending unit.

If one thins epoxy with acetone, soaks a dry float in it, it will become revaltized.

Ed

I just bought a 12v gas gauge. I have the old one out. I know which cable is my sending unit and which is the power so I'm good there. My question is when I install the new gauge, nothing goes behind it before I seat it in the cluster correct? Also I put the "board" piece that says sender and power on the backside of the cluster case before putting on the washers, lock washers and nuts. Is that it? I had a cardboard jumper on the old one but that doesn't seem to be needed.

I just installed a 12v fuel gauge I purchased from Classic Parts and installed nothing between the gauge and the cluster back. From what I’ve read in this forum, the gauge is grounded by touching the back of the cluster housing. The rectangular insulator I installed on the outside of the cluster under the flat washers, insulating the connectors from touching the cluster back and grounding out.

Mine now work perfectly! I hope I didn’t just jinx myself!

Phil