The Stovebolt Site Forums The Shop Area The Electrical Bay Technical question about fuel gauge

Original 6v fuel gauge. Tried ohming between posts on fuel gauge and got "0.L" Every other ohm test on the other three gauges I got some kind of reading. That means, the "0.L" for the fuel gauge is fuel gauge is fried, right?

S2

0 ohms means the circuit is open, so yes...if the posts are clean and the gauge is working right and has good clean leads I'd say you might have a ruined gauge. Try to look carefully at the fine wires which connect to your gauge's posts. You do know there are two different electromagnets in there, yes? Please let me know if this is news to you or if you need more information. There is a file I wrote years ago. I think the title was something like "how your fuel gauge works...sort of."

Edit...the file was "your fuel gauge explained, sort of" (I think)

That is not how you test a gas gauge. Also when testing the gas gauge and the other gauges, were they connected to anything?

Give us some detail, background, history........what are you doing and why.

You are testing with a multimeter, right?

Back in the late eighties ('88, '89) I had changed the pickup to 12V; I had changed the speedo to a rebuilt one but couldn't remember if I had also changed out the cluster gauges or had installed a reducer. I am now in the process of trying to repaint the interior as: 1. tired of the black interior; 2. because it was used as a daily driver after my AF stint and drove it daily to a potash mine to work, the dash and floor got a lot of surface rust (floor rusted so bad am having to replace panels). In order to get the rust off the dash, I found it would be best if I removed the cluster gauges and speedo and using a braided wire wheel and (thinking of) using OSPHO. So I have removed the speedo and cluster gauges; the amps gauge still had the 10 gauge wires hooked to it but the fuel gauge evidently didn't. the nuts that would have been tightened on the posts for the electrical wires were almost all the way off. I read on a post that was done back in 2007 about measuring the ohms for Rl and Rm(?) but really couldn't follow it. But tried taking a reading between the two posts of the amps gauge and fuel gauge. Got readings on the amps gauge but not the fuel. Please understand I DO NOT have access to 6V around me. And the only 12V around me is on the Harley and I hope you won't be telling me to try to tear that apart to use that! So, Jon, no I wasn't aware of the two electromagnets as I haven't take the cage and bezel apart yet. And, bartamos, (there's lots of places "west of the Rio Grande"; which is yours if it's not too personal) I was just trying to see if there was continuity between the two posts of the fuel gauge. However, since I have you guys on the line, my oil gauge has this solid wire soldered to the gauge; the other end (engine) had to be cut to pull the engine; would I be able to melt the solder and re-solder oil pressure wire to it without ruining the gauge because of the heat? To answer another question, both temp and oil gauges have the wire attached (was actually getting continuity through the solid wires) but the amps and fuel gauge weren't attached to anything. Further, I went ahead and ordered a 12V gauge as I already have a 12V sending unit for my new tank and was wondering if my 6V would be useful to anyone. Thank you both for replying so quick; and Jon, will be checking for that file.

S2

1. I guess it's a moot point about the gauge if I read you bought a new one. When you were "ohming" the gas gauge, you were basically testing for resistance or continuity (as you said) on a 8"-12" coiled length of 30 ga wire. That would show about .1 ohm (1/10 ohm) or less. Your multimeter probably is not capable to read that. So it can throw a OL (open loop). It's possible if you use the buzzer mode it may buzz but I think that takes higher ohms to buzz.

2. There is no voltage spec on a sender. They work only to supply a resistance on 6V or 12V or 8V or.....

3. Normally you do not want any wires attached to a component while doing continuity, For sure no power on. Harley is safe. I thought your temp and oil would be mechanical/non electrical, so was confused when it seemed you checked them for continuity.

4. No, the oil pressure unit is toast.

5. To test the gas gauge just use the old or new sender and move float up and down. Use a household 9V battery, just looking for needle to move.

Thank you, bartamos. As far as the oil pressure gauge goes, why would they sale copper and plastic oil pressure line kits. How are those supposed to attach to the gauge?

S2

Compression fittings/ferrule on the new ones on both ends.

So let's back up.... you have a legit point....... you say "the other end" is cut off. I will assume it's copper line that was cut. It's tubing with oil in it, goes up the line to the gauge. Since there is no "sender" on a mechanical oil pressure gauge, it's just a pipe fitting/adapter/bushing/whatever, screwed into a place on motor where oil pressure is present. Usually there are several places that can be used. Maybe you can get a compression fitting on that end. That would work. Leave the gauge end alone because it's soldered. Don't know if that end is salvageable if broken, maybe so. Gotta see some pix. Clean up the cut end, chamfer/deburr it and slip a fitting and ferrule onto it and adapt it up to another fiting that fits the motor hole.

You are rightly speaking of parts like THIS.

You can use an electrical gauge that does have a sender. Good ol resistance signal again. Maybe you have an electrical gauge, You say a "solid wire" is soldered to the gauge. I'm thinking that is tubing.

Isn't 0 ohms an indication of a short, not an open?



Isn't a 0.L (open loop) reading on an ohmmeter indicating MORE ohms than the meter can accurately display, not less?

No, for continuity it means open loop, no connection between probe ends. In voltage testing it can mean over load/over limit if the range is set too low.
I don't know if a multimeter, that can't read 1/10 ohm, will show a OL or a zero. Best to test that gauge as I mentioned.

As far as 0 ohm reading, for what it's worth the internet says. "On a meter, zero ohms (Ω) can indicate a complete circuit or no short. Resistance is a measurement of how well electricity can flow through a circuit, and zero ohms indicates no resistance. A short circuit can also be indicated by a resistance of fewer than two ohms"

My advice, don't test gauges for continuity.

A multimeter that is attempting to display resistance that is lower than the meter's ability (for example 0.0005 ohms on a meter with only 4 digits) should display a zero. Same with a dead short.

A multimeter that is attempting to display resistance that is higher than the meter's ability should display 0.L An example would be a 4 digit meter whose highest displayed number was 3.999 and highest range was 39.99 meg ohms. If you measured a 50 meg ohm resister with such a meter, the meter would display 0.L just as it would if the two meter leads were not touching anything.


I agree


But according to Ohm's law ( I=E/R ) that would mean that any 12 volt circuit that was passing more than 6 amps (ie. a resistance of 2 ohms or less) should be considered a "short circuit".

Bill I see your reasoning.
We should not be trying to 'measuring" anything to test the gas gauge. That is a commentary remark.

The problem with some instructions, for "continuity or resistance testing", is right in the middle of the explanation it starts to talk about "short circuit". What I am talking is ONE wire. Checking it's ends to see if they are connected. We can't check ONE wire for a short by touching both ends with the probes. The instruction mixes in checking a circuit and several wires, if they show continuity to each other, it's a "short". If a wire shows continuity to ground, it's a short. We are not talking that. I am not talking testing a discrete component like a diode and we are not really checking a GAUGE. Most of us use continuity to check ONE wire some place on an old truck. To see if it gets where it is supposed to go. That's it. We are supposed to use the buzzer for that. The instructions throw in zero, OL, L, 1 and talk open, short, out of range, too small to measure and good bye.

You can "check" any old analog electrical gauge that uses resistance as input, using a gas tank sender. Temp gauge, oil pressure gauge, gas......or of course use a rheostat.

First of all, yes...0 ohms, 0.000, whatever indicates a short circuit. Sorry...distracted here and thinking backwards. Thanks for setting that straight, Bill.

Well, guess what I did, folks!!!! I tried to measure continuity on a copper oil pressure tube!!!! Not only that, but also did a continuity test on a bare copper wire that's supposed to carry HEAT!!!
NO shorts were detected! Bartamos, you are absolutely correct, the oil pressure tubing was NOT soldered but it seems the temp gauge wire is. Oil pressure has compression fitting. I found it after cleaning the backside off. The 6V fuel gauge is like Jon said, two separate mini-coils or electromagnets but can't see any way they are connected to each other. Unless it's the brass plate thing on the backside of the posts. And one of the threaded posts is free turning, that mini-coil has scorch marks on the top and the cream colored gauge plate looks like someone put a lighter to it. So definitely wouldn't have gotten continuity out of it any way.
I'm declaring this 6 VOLT fuel gauge is FRIED and this subject CLOSED.

I have learned quite a bit about gauges and multimeter readings (now if I can retain it all, I'll be doing GREAT) and thank ALL those that helped!!!!!

S2

I'm going to lock this thread because the issue at hand was cleared up.

Thank You.

Rusty Rod

That said, I DELETED most of the commentary that does not contribute to the actual ISSUE. (This was advised by Stovebolt HQ).

Apparently, there are unresolved issues that the OP still needs addressed, so I will open this thread again. Please stay on topic and keep the chatter to a minimum. Thank You.