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I'm attempting to install new gas gauge and sender in my 53 3100. I've change over to 12 volts. I assumed I could bench test the new units, but nothing happens when I move the float up & down. The new guage doesn't limit how far the needle will roll and when I gound it out the needle points straight down? Anybody else run into this if so I need your help, thanks.

You can test the sending unit using an ohmmeter. I don't believe the gauge needs grounded. I believe the circuit should be: hot to gauge/gauge to sending unit (using the opposite stud on the gauge)/ground the sending unit. If that isn't correct we'll find out. FYI this will probably get moved to the Electrical Bay forum.

I believe the circuit should be: hot to gauge/gauge to sending unit (using the opposite stud on the gauge)/ground the sending unit. If that isn't correct we'll find out.

that's correct. I like to bench it using the truck wires b4 i screw it down, you should be able to bench test it in the truck b4 you install it in the tank.

The fuel gauge and the sending unit have to be tied to a common ground. The guts of the fuel gauge are comparing the case ground with the sending unit ground...this comparison is what makes the needle move. More ground through case= FULL, more ground through sending unit=EMPTY. I'm pretty sure this is the drill!

Stuart

question, i just installed a brand new sending unit, grounded it to just above the tank. and ran the wire all the way up front to the correct post (i think) on the gauge. but nothing happens. i followed the wiring schematic in my manual, so i'm pretty sure i have the wire from the sending unit in the right place. any clues????

It's pretty easy to break the problem into two pieces. If the gauge is properly powered on one side, and the other side goes to the sending unit, then turn the key ON, pull the sending unit wire (at the sending unit) and the gauge should read FULL. Same deal but ground that wire. Gauge should read EMPTY. If all this works, the gauge and wires are fine and the problem is the sending unit or its connection with ground.

I think this is how it works!

Stuart

would a 12 volt conversion do anything to make it not work? i see some stores sell a voltage reducer just for the gas gauge.

either way i'll ck it out this weekend and report my findings.

so 12v keyed power on one post of the gauge, and on the oposite the signal from the sending unit. and the unit ground. thats all.

Yes...6 volts on 'E' side terminal and sender on 'F' side terminal. Gauge must be grounded through the case in the dash assembly and the sender must be grounded to the system through intimate contact OR a wire from a mounting screw to the body/tank/frame.

If 12 volts was connected to the gauge at some point, there is some chance it was destroyed. This is not a 'for sure'! Folks do evidently run the gauges on a full 12 volts without killing them, but as you have discovered, they do make a voltage reducer intended just for this application.

Remember, grounding is important. That is what makes this system function...or not function. Good luck!

Stuart

ive been without a fuel gauge for some time and recently installed a new fuel sending unit in my 55 6500, am i thinking correctly that the sending unit doesnt care wether the truck is 6 or 12 volt? mine had been converted to 12v. also i already knew that the original gauge was fried so i have what appears to be an aftermarket fuel gauge from the late 60's early 70's. when hooked up with about 3/4 tank of gas it reads past the full mark. i believe the sender is 30 ohm, am i correct in thinking that the gauge must match the sender ohm for ohm to be correct? and if so what is the correct way to test the gauge? the trucks a worker and im just wanting to get by for now.

A Tech Tip by a moderator of this forum.

Bench testing the gauge and sender will let you know if they work before installation. Ground the top of the sender unit (where it is attached to the tank).

The fuel guage thing has always baffeled me. You have a hot wire going to a fuel source and a resistor inside that same fuel source. Duz anyone see a problem here? Electric fuel pumps in the tank bother me also. Can you say BOOM!
Well thats the way they have done it for a long time and I have never heard of one going "BOOM" so I guess its ok.
The guage and sending unit you are using --- are they origional or aftermarket?
The origional type will need a resistor or you will burn the thing out. Most of the origional guages also have what is known as a "vibrator" or "resistor" before the guage and it is usualy attached to the dash or cluster in some way. Even if you have a working vibrator you will need to drop that voltage from 12 to 6 volts before the vibrator. If not you will let the smoke out the guage.
The aftermarket type will usualy take 12 volts (see the instructions) and has a vibrator built in.
Hope this helps-- James.

Toyvo,

While I'm not sure on this, I don't think any AD rigs (or any Chevrolet) used this 'vibrator' in the fuel gauges.

Stuart

Ok i guess then, "Most of the origional guages also have what is known as a "vibrator", does not include chevrolets. Fords,Chryslers,Toyotas,Datsuns(Nissans), Hondas, VW's,Damlers,Bmw's,Audi's,Fiats,Triumps, and M.G.'s before 1974 do. So I guess as Rosanna Rosanna Danna says "Nevermind"!

just found out the fuel sender i got from what use to be chevy duty in parkville,mo is per original spec. 0-30 ohm which will work with any chevrolet truck fuel gauge up to 1967 which is when gm switched to a 0-90 ohm sender and gauge. also the sender is not voltage particular when it comes to having 6 or 12 volts. my original gauge was already toasted, ill get by for now with a 63 truck gauge i have laying around, at least i wont get stranded.