The Stovebolt Site Forums The Shop Area The Electrical Bay Fuel sending unit for 12 volt conversion

Hey Guys,
I converted my 6 volt 1953 3600 to 12 volts. I used a kit that came with what I thought was all of the resistors for the heater and the gauges, etc. My fuel now reads 1/2 tank all the time. I have the part they told me to install on the wire to the gauge. There wasn’t one for the sending unit but I’m thinking there should have been. Is the sending unit in the tank cooked now? Does anyone know what I need to put in the tank for a sending unit to make this work again?
Thanks
Rich

In doing some more research i realize the wire to the sending unit comes for the already reduced fuel gauge. I’m thinking hits is likely the sending unit. It is a replacement unit but is about 20 years old. Just seemed funny that it went right after the 12 volt conversion.

I think I know how to test the gauge and the sending unit electrically. Also maybe the float is stuck.

Just the hot lead to the gauge needs a voltage reducer, not the sender.
Most troubles are that the sender mounting flange is not grounding. The fix for that is to add a wire from a sender screw to a nearby frame spot.
See if that helps. The system is not real accurate. If you have a half tank +/- a 1/4 of a tank it may read 1/2 ish.
If you still want to test them together, it can be done but you will have to pull out the sender.

Thanks I will check the ground. I think I have a separate ground on just about everything…even my tail lights as i have had issues in the past with other trucks. So when I did this one I put a separate ground on all the different components. I get your point on accuracy. It was never very accurate but now it just stays at 1/2 and never moves.

Unfortunately I put a new interior in the truck last year and the gas tank is covered by a panel. I may be able to check the ground but if I have to take the sender out i will have to remove the bucket sets to get the panel off to get the sender out.

Thanks again
Rich

I have a reducer on the gauge. I put a meter on the gauge side of the reducer and with the key off or on I get no voltage.

So I put the meter on the hot wire side of the reducer and I get 12 volts with the key on and no volts with it off.

It appears to me the reducer is bad.

I jumped out the reducer and the gauge went to full with the key on.

It returns to 1/2 when the key is off. It appears the gauge may be stuck and can’t go below half. It used to float a little when driving before the 12 volt conversion.

I also grounded the sender side of the gauge and it stated at 1/2. Didn’t even budge a little.

I called vintage auto for a new reducer. Should I put and aftermarket gauge in. The in dash gauge is only 10 or so years old. Replacing it is a nightmare.

What’s a good after market gauge that will work with my sending unit. I believe the sender is 30 ohm. I bought it from LMC truck with the gauge.

Thanks
Rich

Hi Rich, If the gas gauge is new (even 10 years old) it is very possible the needle is getting stuck on the glass of your gauge cluster. The replacement gauges are well-known to have this problem. The Chinese folks mis-measured them or something. You may even be able to see this happening if you look closely. Honestly your gas gauge will work on 12 volts (mine has been doing so for 40+ years with no reducer). If you decide the needle rubbing on the glass is the problem, one way to fix it is to loosen all 4 nuts holding the cluster to the dash, push it back enough to carefully remove the trim ring and glass panel, carefully remove the rubber ring in the cluster (the one that keeps the glass from rattling) and put something behind it that's about 1 to 1.5mm thick. Could be a ring cut out of a cereal box, a piece of inner tube cut in a ring, whatever. You just want to keep the glass from going in as far as it is right now.

Your fuel gauge isn't fried and that voltage reducer may not even be needed. Please let us know if you can see what the needle is doing.

Jon,
Thanks for the advice. I think the gauge and the sending unit are ok. I am sure the voltage reducer is bad and you are probably right about the needle sticking on the glass. I tried to pound on it a bit but it won’t move. These gauges are a pain to remove but I drive in a lot of remote areas. I really need some indication of how much fuel I have. I know these aren’t that accurate but at least it’s something.

I will try the spacer behind the glass and let you know.
Thanks again!
Rich

Just and update
So I removed the gauge cluster … my least favorite job… and took the reducer off then direct connected the 12 volt wire to the fuel gauge. I then removed the bezel and filed down the little lip on the gauge face (where it says Fuel) as it seemed to be touching the needle.

If I turn the key on the gauge goes to full (the tank is full). If I ground the gauge out it goes to empty. The needle still hangs at about 1/2 with the key off and the gauge in place. I am hoping that when the fuel level drops the gauge will drop as well with the key on.

I know these gauges aren’t that accurate but if i can get it to do what it did before, basically showing above 1/2 when it is above 1/2 and showing below 1/2 when it is below 1/2. So at least I know I need to get gas when the gauge drops below 1/2. I think the whole problem was the reducer. I should have just removed that and left the gauge cluster alone.

I did notice a tiny bit of oil as I was reinstalling the gauge cluster. I am just hoping I didn't damage the oil pressure tube. That would really make my week.

Yes, we hope you didn't damage the oil pressure tube but the likelihood of that is not great...hopefully. Please keep us updated on progress, etc.