23 replies to this topic

[Tomf]

Well i have have just fitted my new dash and i have used different gauges throughout, however the fuel gauge that i fitted doesn't work at all, im not sure if i wired it in correctly. I used the green and black wire from on the block that plugs into the standard mini clocks, and earthed the other terminal on the fuel gauge, this didnt work so i switched the terminals round and still the gauge didnt work....

To check if the gauge even worked at all i put a 12v feed through it and the needle moved up as if to show that the tank is full.

So does anyone know what i have done wrong, i though that even if the sender wasnt correct for the gauge that it would at least move a bit.

Someone please help me.

Tom

[Dan]

You've assumed the fuel gauge you have bought uses the same sender unit as the original for one thing. What type of gauge is it?

[Tomf]

To be honest im not really sure what gauge it is lol. its part of a 3.75" gauge that also uses water temp and oil pressure. It looks like an old gauge, looks the same as my 52mm smiths gauges but alot bigger lol and its not smiths. If it is the case of the sender not working with the fuel gauge, what options do i have, do i have to just buy a new gauge?

[Tomf]

As an alternative to the gauge already have, as i think the sender is wrong, does anyone know if any of these fuel gauges will work with the sender:

Ebay link it says mini in the title but also says other cars...

Ebay link

Edited by Tomf, 31 May 2007 - 10:34 AM.

[dklawson]

A lot of the early triple-gauges like you described were used on Triumph and Morris models before the voltage stabilizer was added to the gauge system. Any fuel gauge made prior to the use of the stabilizer won't be compatible with the post-1964 Mini fuel sending unit.

Quick question: When you were testing the fuel gauge portion of this 3-3/4" gauge, did the needle move quickly or did it slowly rise? If the needle can bounce around, and if the needle moves very quickly when you test the gauge, it isn't suitable for use with the late model sending unit.

The eBay links were for a fairly typical looking late model Smiths gauge. Those are bimetallic and respond slowly to changes at the sending unit. The basic hook up for this and other compatible gauges is: One spade (Lucar) connector on the gauge gets connected to the output of the voltage stabilizer ("I" terminal on the stabilizer). The other spade lug on the gauge goes off to the sending unit. The sending unit must have a good clean ground connection.

[syholl]

You have connected it up incorrectly for a start.

Mini fuel gauge senders (the bit in the tank) work by providing a resistive path to earth. The more fuel in the tank, the less resistance there is, so the fuel gauge registers higher.

By connecting the other terminal on the gauge to earth, you have essentailly connected both terminals to earth, so it won't work.

Once side of the gauge needs to be connected to the fuel sender on the tank, the other side needs a regulated supply (usually around 10v). You can buy a small regulator chip that does this if necessary. Type in smiths regulator on ebay and you should come across a bloke that sells these if you are unsure.

Not sure what the green and black wire is on the clocks, as i don't use Mini looms on any of my cars, but you can test it quite easily with a multimeter to see if it is the one from the sender.

[Dan]

Ah, yes. I misread the first post and thought you'd earthed the other terminal on the sender which would be correct, but if you've earthed the other terminal on the gauge it will never work. As above all the gauges are earth sensing, not supply sensing. Whether it needs a regulated supply or not and whether it is compatible with the sender is still dependant on what gauge it is exactly, but generally they are all earth sensing AFAIK.

[Tomf]

AH ok i think understand, so do i need to plug my fuel gauge feed to one of the terminals then plug a 10V supply to the other terminal? Also could i get the regulator out of my old fuel gauge, or does it not work like that?

Also when i plugged the 12V feed in with an earth the other terminal, the needle slowly moved up, about the same speed as the normal mini fuel gauge.

[dklawson]

The slow needle movement confirms this is a later type, bimetallic gauge. That's good. Most (but not all) are calibrated to work with a 240 Ohms = empty, to 30 Ohms = Full sending unit.

As stated in various posts above, output from the stabilizer's "I" terminal goes to one of the fuel gauge' spade lugs (either one). The second gauge spade lug gets the green/black wire which goes off to the insulated terminal on the fuel sending unit. The second (earthed) terminal on the sending unit gets a black wire which goes off to chassis ground.

As far as using the old stabilizer, I can't tell you where they are on cars after the Mk3s. However, they won't be in the gauge. On the older cars these were typically little horizontally mounted rectangular metal cans about 25mm long by 16mm high and perhaps 12mm deep. They will have two spade lugs on them, "B" for switched 12V input power, and "I" for 10V output power to the gauges. The stabilizer case MUST be connected to chassis ground to work.

[Tomf]

Thank you for the help , so as the fuel tank is already earthed i should just have to take the feed from the green/black wire and this should go to one of the spade connectors, then if i but this and connect it up to the other terminal on the fuel gauge, then should it work then?

[syholl]

Yep, that should do it. I always fit that sort of thing on my cars, as they are far more accurate than the old smiths type regulators. Make sure you attach the top of the chip to a metal surface that will dissipate the heat. Shouldn't really be a problem with such a small current draw, but it is best to be safe.

[Tomf]

Thanks ill order that and see how i get on

[dklawson]

The Mini sending unit should have a black ground wire attached to the non-insulated spade terminal. Just make sure that is in place and that the other end of the wire makes a good ground connection. Don't automatically assume that without the wire the tank will be grounded.

That's a very fair price on the voltage regulator you provided the link to. I use the u7810 chip to make my own. From some sources the chip is less than $1 (1/2 GPB). For the seller to offer the chip with leads already on it at 1.5 GBP is great. I'd buy one without hesitation.

[Tomf]

£1.50? they are £12.99 + P&P... is it a good price or are they ripping me off?

[dklawson]

OOPS !!! I'm sorry, I picked up on the shipping charges, not the chip charges.

Yes, 13 GBP is a bit steep for that. I can't tell you where to buy the chip in the U.K. but you're looking for a u7810 chip. As is shown on the auction picture, it's a 3-leaded solid state voltage regulator rated for a fixed 10V. They supply up to 1 amp. The mounting tab is also "ground/earth" so the ring terminal shown on the picture is redundant if you mount it using the hole in the tab.

Download my PDF about it:
http://home.mindspri...eStabilizer.pdf
You can easily make your own stabilizer for a lot less than 13 GBP once you locate a source for the chip. You can also use the more common LM317 regulator with feedback resistors but you have to mount that one differently.