(Another) Fuel Gauge question...

What is the voltage at the power terminal when the charge light is on and when the light is off?

Yeah, I'm guessing that you should see about 11.8V with the charge light on and about 13.2V with the light off.  However there is some interesting pseudo-grounding going on with that circuit because of the way the alternator field circuit works, so that is why most car/dash/instrument designers usually run a separate (dedicated) +12V line to the charging light.

I would seriously move the +12V for your fuel sender to a more stable source, like the IGN on or ALT on side of the key switch.

Just been back out..

Ignition on, (charge light on) voltage is 1.85v (yep 1.85)........Start the engine, charge light out, voltage jumps to 14v.

Gauge looks about right with the lower voltage.....

{I'm running an alternator, if that makes a difference)

You're trying to power your fuel gauge from the "grounded" side of the alternator light. Do as Gordon suggested and find a switched 12V source for power.

OK, with a switched 12v supply, I get a high reading all the time, ( its got exactly 2 (UK) gallons in and its showing 1/2 full)

With the lower voltage applied, (when I had it wired wrong), it was showing 1/4 full which is about spot on.......

So.........How can I feed my gauge 1.85 volts all the time ! I've been reading up on Beetle gauges, they used Vibrators/stabilisers, should I have one of them somewhere?

What does the gauge show (key on, powered with 12V) when you disconnect the wire from the sender (don't let it touch anything)? What does the gauge show if you now ground the sender wire?

Once you have proper voltage, isn't your problem that the sending units for the different gauges require different resistance.  The 914 tube gauge (too long for a bug tank) is 70 Ohms empty and 3 Ohms FULL while the bug one is 75 empty and 10 FULL.  Here's link to rewinding the gauge sensor that might help those that want more accurate readings.

http://www.thesamba.com/vw/forum/viewtopic.php?t=380693&postdays=0&postorder=asc&start=0

Soooo Some more digging around on here says that the Ghia tube sender should do the job...

Any experience of this before buy one?

https://www.speedsterowners.com...ender-for-914-gauges

That's a great link, Wolfgang. It ought to be put up every time this topic comes up.

Have you confirmed that your current sender is broken or the wrong Ohms range? If not, why jump to replacing parts?

What Ohm range does your sender have? Pull it out and measure it throughout the range of float movement, but especially at both empty and full.

You still need to answer my previous questions to verify the gauge is working as expected.

The other thing to check is all your ground connections for the gauge and sender.

Yup easy to see if old sender is bad (the resistive wire wears and breaks).  A cheap $2.99 Harbor Freight Volt-Ohm meter.  Measure resistance when moving the arm (sender out of tank).  If open (no reading) then there is a break.  You want 70 when arm down (empty) and 10 or less when up (full).

I was looking at Auto meter and Stewart-warner gages and senders  a good one should read 240 ohms at empty and 33 ohms at full.  Seams to be the standard for  those brands  I suspect VDO is no different.

Actually, there's a LOT of difference between Stewart-Warner and VDO gauge senders, so it's best to stick with those designed for whatever gauge head you have.

I'm pretty sure that Wild Bill Drayer, on here, used a Ghia fuel sender on his car, and you can email him at wdd4255 at comcast.net to see what it was.

Yes, 240-33 is generally standard on aftermarket gauges. So if you order a gauge and sender combo, that's probably what you'll get. But those gauges can be ordered to match the OEM sender. Here's some common OEM empty-full ranges:

0-30

0-90

90-0

75-10 <- stock for VW/Ghia/914 gauges & senders

10-70

16-158

10-180

240-33

The sender's Ohms range must match the gauge's for it to work right.

ok, heres where I'm at....

I have a multimeter, but my knowledge is limited couldn't work out ohms

I did manage to get a solid 12v, charge light on or off

Justinh,

sender feed disconnected....nothing

sender feed grounded.....gauge registers full

I know there is 2 UK gallons in the tank, cause I measured it back in...... that  should be 1/4 full. so I sat the wife in the car, pulled the sender, and adjusted the arm so that it reads 1/4 full, Based on that, I know I have around 50 miles when it shows 1/4 !!

Also, after some reading of old CMC manuals, I have an admission.........I put the tank in the wrong way around ........

In my defense, for UK regs, I had to put use a 1302 tank and an external filler, that put the fill point top left and sitting level (seemed correct). External filler was a PITA due to odd angles and had problems getting a good seal, it always leaked a little on fill up. Also, I used old school celulose paint (don't know the US equivalent,,,) Unfortunately modern fuels mark the paint........So, at the weekend I dropped in the pre 67, internal fill tank I had. Putting it in the same as the 1302 tank.......(fill point top left). This involved some massaging with a big stick !

Having realized may mistake, (too late), I went out today and got a new tank.....At some point I'll get the neck shortened and fit a ghia tube sender, (if thats the easy way out,,,)

for the moment I can live with knowing when I'm at 2 gallons !

 Cheers

Gerry

 There are 2 versions of that  tube sender  I know one is 11-1/2  type 3  Too long for a bug tank . I think  you need the 9-/14 version . I'm thinking Ghia   But im not sure what its from

Multimeter: plug the red lead into the port marked Ω it should just be the same one you plugged into for Voltage. Turn the dial to the Ω symbol. If it is not an auto-ranging meter and you need to pick the ohms range, pick the one without any K (thousands) or M (millions) after the number. Resistance measurement is non-directional so it doesn't matter what lead goes on what sender terminal.

I assume "disconnected....nothing" means Empty, in which case your gauge seems to be working fine. It also tells you that the Ohms range for your gauge is high-low for empty-full (such as for the standard 75-10).

Did you bend the float arm for 1/4 tank when you had the gauge powered from only 1.85V or from 12V? If you did it with only the 1.85V, rebend the float arm when it is powered with 12V. If you did it now with 12V, that's a decent enough calibration for your use, assuming empty and full also check out (either with gas or a multimeter).

Downside of those tube-type senders is that you cannot adjust them as simply as you did with your float style. You'll have to live with whatever the gauge reads with 2 gallons in the tank.

Thanks for the Tutorial ! I'll try again later today

I got the solid 12v before I did my "adjusting"

Its all of the little things that enrich the experience

Thanks again Team !