8 replies to this topic

[Estate73]

I have just fitted a new dashboard with smiths instruments and the fuel gauge reads backwards. Empty when full, then shows full when empty.

Also the smiths speedo is not working , I think this is a wiring or signal problem from the sensor unit.

Any help would be greatly appreciated

Ta

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[nicklouse]

Sounds like you have the wrong fuel guage.

Standard speedo is a mechanical drive. What is the custom one? Same or is there a box of magic that converts to a electrical drive?

or.....

I would be asking the company that you bought them from.

[Spider]

In regards to the fuel gauge, check that the sender is sending the right 'info'. Use a meter and establish if when full it has a low resistance (about 15 ohms) and empty, a higher resistance (about 240 ohms). If that checks out then I'd be questioning the supplier of the gauge, however the gauges for the very early cars did work that way, ie they would read full on high resistance and empty on low res.

 

in regards to the speedo, is it an electronic one of mechanical?

 

If it's electronic, what sensor are you using and how have you wired it?

 

If it's mechanical, check the cable spins if the car (or one front wheel for that matter) is moving.

[Estate73]

Thanks guys

The speedo is electronic and wired to a sender unit that replaces the cable mechanical system.

The gauges are supposed to be for a classic mini but I'm starting to wonder. I will contact the supplier this week and ask them a few questions. There quite a big company so that might help.

Once again thanks for the help

John  image.jpg   54.82K   0 downloads

[Spider]

What sort of sender for the speedo do you have?

 

Has it got 2 wires or 3?

[dklawson]

Regardless of sender type, the speedometer will have to be programmed to match the output of the sending unit.  Your gauge should include instructions on how to set the number of pulses-per-mile that your car is delivering.

[Estate73]

Hi guys

I wired the fuel gauge to the existing wiring which is basically one wire and a ground, as for the speedo can't get to the setting stage as I think it's not receiving the signal correctly from the sender.

I will get the info required over the weekend to see what type the sender is etc for the fuel gauge. The speedo has three wires black, red and white.

Thanks for the help, very new to all this so once again very appreciated

John

[dklawson]

The speedometer should have black for power, red for earth.  White could be a couple of things... illumination... or the input/sense wire from the sending unit.  Double check your speedometer documentation.

 

As Spider asked, pay attention to the type of speedo sending unit you have.  2-wire senders are typically magnetic pulse devices and require different connections than the 3-wire devices.  3-wire sending units typically work like a transistor where you have power in, earth, and a third wire that is either supplying 12 volts or a path to earth.  You have to know what you have and set up your gauge accordingly.

 

You said these gauges were supposed to be Mini compatible but the fuel gauge is reading backwards.  Double check your fuel gauge documentation again.  The Mini fuel sending unit used on cars after 1964 works in the direction and resistance range that Spider mentioned.  There are several different industry-standard sending unit ranges available.  I would not be surprised to find your gauge is not designed for 15-240 Ohms (full to empty) but is probably designed for 90-10 Ohms (full to empty) as that is another common resistance range.

 

If you get overwhelmed by this and cannot exchange the fuel gauge for one that is compatible you will need to visit the Spiyda Design web site and buy a product like their gauge wizard which will allow generally incompatible gauges and sending units to work together.

Spiyda Design Web Site

[Spider]

As Doug has said, the Speedo Sender needs power (I have the same one in one of my cars).

 

Red +ve 12 V (via the key)

Black  Earth

White is the signal

 

Set it up and test it on the bench, then fit it up.

 

If you go in to the calibration mode, and set the numbers around 5500 that should be a reasonable starting point. You can fine tune it with a GPS and that will be quite OK, however it's best if you go for a drive or at least a known 50 km / miles and then set it from the Odometer readings. I have a formula (somewhere!) for working it out - if I can do it, it's not hard!