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MG MGA - Sender calibration

Does anyone (Barney?) have a calibration of the tank sender display unit? I mean reading vs mA current? How many mA for full and empty readings? I'm thinking mabe an external resistor network could be employed to linearize the tank unit output.
Art Pearse

Find the electrical schematic with resistance values here:
http://mgaguru.com/mgtech/electric/fg_05.htm#fg_diag

The sender unit should be 0-ohms when empty, about 70-ohms when full, and roughly linear in between. If you know how to work resistor networks you can calculate the watts ad mili-ampers.

The gauge is somewhat non-linear, which you can see by the scale markings on the face. One of the adjustments is effectively a linearity adjustment. Response of the gauge is changed considerably with only minor adjustment of the magnet positions. You might fiddle all day with external resistor networks, and then the smallest adjustment of the magnet positions would screw it all up anyway. It is probably a lost cause.

Barney Gaylord

Wow. I thought it was just a modified ammeter!
Art Pearse

Art,

it's not difficult to calibrate both the sender unit and the fuel gauge if you follow Barney's instructions. You will find that his instructions are very easy to understand and follow. Following Barney's instructions to the letter, I managed to calibrate my instruments to original specs. I've had no problems reading the amount of fuel in my tank ever since.

Frank
F Camilleri

Installed new sending unit with stamp "Top" oriented at top on 58 MGA. Connected it with existing electrical wire. Battery is positive ground [as per schematic]. Tank is empty but when key is on gauge registers "F". Is it a polarity problem or calibration? How do I determine?
W. Berry

Disconnected or open circuit (or resistance higher than 70 ohms) on the sender wire will drive the gauge needle hard against the "F" peg. Loss of grounding of the fuel tank will do the same. Fuel tank was originally grounded through the steel pipe from tank to pump, with a grounding wire on the pump. If you have rubber hose connection to the fuel pump, then add a ground wire from the sender unit to a tab on the frame nearby.
Barney Gaylord

I just discovered my fuel gauge is no good as well. Open circuit and loose magnets.
Art Pearse

Hi Guys

Just to add my twocentsworth.
The sender does not send the true tank condition in its standard form.
The float hits the base of the tank before the gauge reads empty. The float never reaches the top of the tank, that's why when filled up the gauge needle stays at 'full' for some time until the level reaches the maximum float position.
I have lengthened the wire arm and bent it to achieve the full sweep of the tank.
I found that calibration of the gauge was unneccesary.
I have yet to send the details to Barney, so that you all could do the modification.

Phil
P J Whittington

Mr. Berry
I just had exactly the same problem. I fixed it with a ground wire from one of the six cover bolts, of the sender unit, to the chassis ground connection beside the tank. Instant repair.
Gordon Harrison

This thread was discussed between 30/04/2013 and 17/05/2013

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