105 Fuel Gauge Problem

[njh1964]

Hi All,

I realise this topic has been discussed in previous posts, but nothing seems to exactly cover the problem I'm experiencing with the fuel gauge in my 1968 GT1300 Junior, which is a first series 105 with the flat dash and Veglia gauges.

Problems:

1. The low fuel warning light on the fuel gauge does not come on when the tank is empty.

2. When I switch on the ignition, the fuel gauge needle goes straight to the full position, and it stays there. The needle did this before I put any fuel in the tank, and it did the same after put about quarter of a tank of fuel in.

Tried so far:

Firstly, the gauge seems to be powering up correctly, and there's an earth wire attached to the rear of the gauge. Also, the gauge backlight is working OK.

I've tried disconnecting the earth wire from the back of the gauge (suggested in a previous post), but this makes no difference.

I wasn't sure which terminal on the sender unit was for fuel level and which was for low fuel warning, so I've tried swapping the two wires between the two sender unit terminals.

Even when the tank was completely empty, nothing happened with the low fuel warning light regardless of which terminal it was connected to. I've checked the low fuel warning light bulb in the gauge, and it is working fine.

I've installed a brand new fuel sender from one of the UK suppliers, and I did specify a Veglia sender (ie not Jaeger sender) when ordering. I assume I did actually receive a Veglia sender because it has what I think is the correct "01006" part number stamped on the rim.

I've attached an earth lead to one of the mounting screws on the sender unit, and then to the bodywork... still no joy.

I've checked the two wires (ie fuel level and low warning) between the gauge and the sender unit with a multimeter, and they're both fine.

What an I missing? Faulty gauge, incorrect sender unit, etc?

Regards,


Nick

[310]

try this test
1.pull sender unit out
2. disconnect the fuel gauge
3. connect multimeter to fuel sender wiring
4. power up fuel sender unit needs to earthed
5. check the ohms on the fuel sender unit from empty to half to full by moving the float manually ( record your reading)
6. now check the fuel gauge end and compare the readings every time you move the float the reading should change if you are getting a reading then it means that the problem is in the gauge.

when the ignition is on there should be b+ on fuel gauge and low fuel light connection to fuel tank, also check your earth to fuel sender unit a good earth.

[LaStregaNera]

I had this problem when I first put mine back together - Add an earth from the sender plate on the tank to the body shell - from memory that's how I fixed it.

[ItalCarGuy]

it is almost always a bad earth so I am surprised that running a wire from under a screw on the sender to the body didn't fix it. I  had to do this again a few weeks back as mine was reading like yours.

[Gary Pearce]

Gee........ that's a complicated way of testing the fuel gauge Enzo.
Best test procedure:
Pull the mat out of the boot.
Pull both wires off the fuel tank sender unit in the boot (usually white and yellow)
Turn the ignition on
Short out to earth, first one wire in the boot then the other.....either the low fuel warning will come on or the fuel gauge will deflect depending on which wire.
That should then help you determine if you have an earth problem, a fuel sender problem or a gauge/wiring problem.



















9

[310]

sorry did not mean to make it sound hard it's the mechanic in me thinking out loud.

[njh1964]

Gee........ that's a complicated way of testing the fuel gauge Enzo.
Best test procedure:
Pull the mat out of the boot.
Pull both wires off the fuel tank sender unit in the boot (usually white and yellow)
Turn the ignition on
Short out to earth, first one wire in the boot then the other.....either the low fuel warning will come on or the fuel gauge will deflect depending on which wire.
That should then help you determine if you have an earth problem, a fuel sender problem or a gauge/wiring problem.

Hi Gary,

Thanks, I'll give that a try. I did appreciate Ezno's suggestions (thanks, Enzo), but I'm a bit of a novice when it comes to operating a multimeter, which is probably a shortcoming I should also address.

Regards,


Nick