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Defender fuel gauge 1995 model 300Tdi


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#1 BogMonster

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Posted 25 June 2011 - 01:32 PM

Looking at a Defender 90, 1995 model year, 300Tdi, standard 90 side fuel tank under driver's seat.

The fuel gauge isn't working at all - needle doesn't move. I suspect the sender unit may have gone but looking at the wiring, there are two wires onto the top of the tank sender unit. The connector face view in RAVE gives me C880 (GB wire) and C660 (B wire). C880 is a wire running to the gauge (green and black), while C660 is ... nothing! Not shown on any of the wiring diagrams if you do a search for it. Not sure if it is supposed to be an earth for the sender (possible being black, but no earth wire is shown on the circuit diagram), or a feed for a low fuel warning light, or what.

Does anybody know offhand if the gauge will mind if I short one (or both) of these to earth i.e. does it make a perfect earth to show full fuel, or perfect earth to show empty fuel, or what is the resistance range for the gauge in normal operation from full to empty? Not helping is that I also have no idea how much fuel is in the tank at the moment :rolleyes:

Thanks ;)
2002 Discovery II 4.0 V8 auto • 2006 Defender 110 SW 300Tdi • 2011 Ford Ranger XLT crewcab

#2 western

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Posted 25 June 2011 - 02:06 PM

C660 is earth goes to the blue header via these other connectors according to the earth distribution page [see below. highligthted in green]

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#3 Retroanaconda

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Posted 25 June 2011 - 02:06 PM

If you short the GB wire to earth it should show full, ie. full deflection on the gauge. Won't harm the gauge.

The B wire will most likely be the earth, since the fuel tank mountings can't be relied upon to give a decent earth the sender earths through this wire back into the loom and to one of the earth headers. It could be a low fuel light, but that is a different colour I'm sure. My 90 (a 200Tdi) doesn't have a low fuel light connection on the sender, it was instead provided through a 'device' I found wrapped up behind the dash, which the fuel level signal was passed through. I can only assume this read said signal and provided a fuel light signal when needed. Now this has been removed and the Td5 speedo head provides the same function.

#4 BogMonster

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Posted 25 June 2011 - 03:23 PM

C660 is earth goes to the blue header via these other connectors according to the earth distribution page [see below. highligthted in green]

Thanks Ralph, doesn't actually say it is C660 on the diagram which I guess is why it didn't show up when I searched the PDF for "C660" (usually a reliable way to find all references to it) but I reckon you're right - it's on a black wire so fairly sure to be the same circuit. I'm not even sure if the early 300s have a low fuel light so that was just a possibility but looking at that I'd say its an earth so I'll check that and see. Hopefully a new sender ain't too expensive if it is that...

Time to break out the multimeter!

Ta ;)
2002 Discovery II 4.0 V8 auto • 2006 Defender 110 SW 300Tdi • 2011 Ford Ranger XLT crewcab

#5 western

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Posted 25 June 2011 - 03:44 PM

not all 300tdi vehicles had a low fuel warning, most UK 300tdi didn't.
C660 is shown in the list of connections in the Rave 300tdi electrical library, I forgot to add the page, see below, should confirm you ahve the correct wire/connector.

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#6 BogMonster

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Posted 25 June 2011 - 07:47 PM

Problem located - about a 150 ohm resistance somewhere in the GB wire between the sender and gauge, got about 50 gnomes at the sender and about 200 gnomes at the gauge so it's not moving. Run a bypass and it works fine, shows half a tank, so I guess I'll just put in a permanent replacement wire as I can't be f'ed to pick the harness to bits, it isn't the connector in the engine bay so it must be a break inside the wire somewhere.

Ta :)
2002 Discovery II 4.0 V8 auto • 2006 Defender 110 SW 300Tdi • 2011 Ford Ranger XLT crewcab

#7 western

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Posted 25 June 2011 - 08:09 PM

glad you found the fault & engineered a cure, a good days work in all :D
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#8 BogMonster

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Posted 26 June 2011 - 07:16 PM

Problem solved - ran a new wire from the sender straight into the back of the gauge and all works fine now, and much easier than messing round looking for wiring faults :)
2002 Discovery II 4.0 V8 auto • 2006 Defender 110 SW 300Tdi • 2011 Ford Ranger XLT crewcab




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