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MG MGA - Faulty Fuel Gauge or me being a bit thick?

Hi guys,

I've converted my A to Negative earth as it's got an alternator and a modified engine amongst other things during a full rebulid.

Now that it's coming to the end of the rebuild, I've started to check the little things, and I've noticed that the fuel gauge (original Jaeger) is reading less than empty when the tank is anything but empty.

I've changed the sender unit from the original one to a modern Moss one (just in case it was broken), and still the same, reading less than zero when full (stupidly I didn't check when it was empty).

Being I've changed from Positive to Negatige earth, does this cause the gauge to work backwards? Do I need to do a bit of rewiring, or do I need to get the gauge modified for use on Negative earth?

Many thanks in advance,

Grant
G Hudson

The MGA fuel gauge is not polarity sensitive. If you kill input power the needle will go to rest against the "E" peg (a function of gravity). If you disconnect the "T" terminal the needle will go hard against the "F" peg. If you short the "T" terminal to ground, the needle should point directly to the "E mark (not against the peg).

When not functioning properly, disconnect the "T" terminal and test the gauge and sender unit separately. For function and testing information see here:
http://mgaguru.com/mgtech/electric/electr_1.htm
http://mgaguru.com/mgtech/electric/fg_01.htm
http://mgaguru.com/mgtech/electric/fg_06.htm
http://mgaguru.com/mgtech/electric/circ_f1b.htm
http://mgaguru.com/mgtech/electric/fg104.htm
http://mgaguru.com/mgtech/electric/fg110.htm
barneymg

Hi Barney!

I'm honoured to get a response from the guru himself! :-)

I took a look at your site and followed the testing for the senders (both fitted the bounding figures on your website and were +/- 2.5 ohms of each other), which made me think it's the gauge. On re-reading your info, I'll run an additional earth for starters as it might be a bad earth problem, otherwise I'll ship it off to get looked at.

Many thanks,

Grant
G Hudson

This thread was discussed on 02/07/2018

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