reb78 Posted October 1, 2009 Share Posted October 1, 2009 Just a quick one. Its probably an earth issue, but my fuel light is always on (the tank is full). The gauge works fine and is as accurate as they are. Does the feed for the fuel light come off of the gauge or is the fault likely to be elsewhere? Its been like this for ages and used to go bright when full, then dim, then off when about half full, then bright again when nearing empty. Its just on all the time now though. Thanks Quote Link to comment Share on other sites More sharing options...
crwoody Posted October 1, 2009 Share Posted October 1, 2009 If it's a td5, (I don't know about the others,) the fuel and temp gauges and the speedo share a common earth (black,) they also share a common live feed too (white/green.) The fuel sender unit is connected to the gauge via the low fuel lamp (grn/blk - blk/grn.) So that leaves me a little puzzled as to how the gauge can work normally but the lamp malfunctions? Quote Link to comment Share on other sites More sharing options...
crwoody Posted October 1, 2009 Share Posted October 1, 2009 Still not sure which yours is but I've just managed to find a 300tdi wiring diagram which shows a seperate "Low fuel level unit", a seperate module driving the lamp directly (white/slate?(grey) to [1]), it appears to have it's own earth connection seperate from the gauge so maybe that is the answer. I couldn't tell you where the module is though, but at a guess it's likely to be close to the instrument panel. Quote Link to comment Share on other sites More sharing options...
reb78 Posted October 1, 2009 Author Share Posted October 1, 2009 If it's a td5, (I don't know about the others,) the fuel and temp gauges and the speedo share a common earth (black,) they also share a common live feed too (white/green.) The fuel sender unit is connected to the gauge via the low fuel lamp (grn/blk - blk/grn.) So that leaves me a little puzzled as to how the gauge can work normally but the lamp malfunctions? Thanks for that. That is puzzling. Its a Turbo Diesel setup (200tdi fitted) but the rest is TD. Even so, would have thought the wiring was a similar setup. If the light got its feed from the gauge then i could understand the gauge working fone and a fault after, but not the other way round! Quote Link to comment Share on other sites More sharing options...
reb78 Posted October 1, 2009 Author Share Posted October 1, 2009 Just seen the second post. I will investigate for an earth linked to the light and see if i can find what might be a low level sender unit. Quote Link to comment Share on other sites More sharing options...
western Posted October 1, 2009 Share Posted October 1, 2009 Thanks for that. That is puzzling. Its a Turbo Diesel setup (200tdi fitted) but the rest is TD. Even so, would have thought the wiring was a similar setup. If the light got its feed from the gauge then i could understand the gauge working fone and a fault after, but not the other way round! My 110 was a TD now a 200Tdi, the low fuel light is switched by the tank sender unit & IIRC there's a relay behind the instrument pack to the right side screwed to the underside of the inner cowling, could be that is faulty or the tank unit is duff or the low fuel wire is shorting out on the chassis & earhing itself. Quote Link to comment Share on other sites More sharing options...
errol209 Posted October 1, 2009 Share Posted October 1, 2009 ... its quite a common fault then, 'coz mine does it too (on when full, off between 7/8 and 1/3 full, then on solidly below 1/4. Quote Link to comment Share on other sites More sharing options...
bishbosh Posted October 1, 2009 Share Posted October 1, 2009 There's a low fuel light....??????? Quote Link to comment Share on other sites More sharing options...
errol209 Posted October 1, 2009 Share Posted October 1, 2009 There's a low fuel light? Mr Bosh's bulb economy drive knows no bounds ... 1 Quote Link to comment Share on other sites More sharing options...
reb78 Posted October 1, 2009 Author Share Posted October 1, 2009 Its not too much of a worry, just something i hope will be a quick fix when i get 5 mins (yeah right - its a land rover!). If its likely to be the fuel pick up/sender in the tank, i ahve a spare, so might try replacing that first - just couldnt figure out why the gauge would work if the sender was faulty. Quote Link to comment Share on other sites More sharing options...
western Posted October 1, 2009 Share Posted October 1, 2009 you could just disconnect the wire at the sender unit & safely secure it, so the flicking light doesn't distract you. Quote Link to comment Share on other sites More sharing options...
western Posted October 1, 2009 Share Posted October 1, 2009 There's a low fuel light....??????? Yep, but not all tank units have the required connection. Quote Link to comment Share on other sites More sharing options...
dailysleaze Posted October 1, 2009 Share Posted October 1, 2009 I've got exactly the same problem on my 200Tdi. Thought it might have been a bad earth, but there's only 2 wires from the tank, so the sender can't be powering a low fuel warning light as well as the gauge. I've reseated all the earthing points at the rear and still no joy. My 110 was a TD now a 200Tdi, the low fuel light is switched by the tank sender unit & IIRC there's a relay behind the instrument pack to the right side screwed to the underside of the inner cowling, could be that is faulty or the tank unit is duff or the low fuel wire is shorting out on the chassis & earhing itself. I've wondered what that relay behind the dash was for. Mine's a bit loose so it might be that. The light being on wasn't an issue until I fitted a Td5 instrument panel and now it's quite distracting! (I guess that's why it's so bright...) Quote Link to comment Share on other sites More sharing options...
Puffernutter Posted October 1, 2009 Share Posted October 1, 2009 you could just disconnect the wire at the sender unit & safely secure it, so the flicking light doesn't distract you. If you disconnect the wire at the sender, you could rule out a short circuit further up the line. If it's disconnected and still stays on, the problem may well be behind the dash. Cheers Peter Quote Link to comment Share on other sites More sharing options...
western Posted October 1, 2009 Share Posted October 1, 2009 I've got exactly the same problem on my 200Tdi. Thought it might have been a bad earth, but there's only 2 wires from the tank, so the sender can't be powering a low fuel warning light as well as the gauge. I've reseated all the earthing points at the rear and still no joy. not strictly correct, some tank senders have 2 connections [fuel gauge signal & earth, others have 3 connections, fuel gauge signal,earth & low fuel warning -- my 110 has a 3 wire sender & a warning light on the dash] I've wondered what that relay behind the dash was for. Mine's a bit loose so it might be that. The light being on wasn't an issue until I fitted a Td5 instrument panel and now it's quite distracting! (I guess that's why it's so bright...) Td5 low fuel light is controlled by the speedo [internal circuit] Quote Link to comment Share on other sites More sharing options...
crispyduck Posted April 22, 2016 Share Posted April 22, 2016 Better a late reply than none. I found taped up in the main loom behind the instrument panel of my '93 110 this little pcb driving the low fuel light. It's a comparator circuit that triggers at a certain value from fuel level sensor. The wire coming from the low fuel connector on the tank sender was grounded at the rear LHS lighting ground point. Everything was untouched so I guess it's another example of Solihull's sense of humour Quote Link to comment Share on other sites More sharing options...
nileseh Posted December 5, 2021 Share Posted December 5, 2021 And so now 5 years later continued..... Obviously not a pressing issue, but the last post is correct. The small circuit is embedded in the harness so not intended to be a serviceable item. In any case there does not seem to be a replacement source. I'd call that a limited sense of humor. The device in my '93 110 seems to have failed, but it suffers from visible corrosion on some of the traces so I may be able to clean it up and perhaps recover operation. However, I removed it from the harness and inserted a 4-pin connector. If I get it to work I'll be able to plug it in and motor on. If I can't get it to work, I did some measuring, extrapolated the data and determined that the the resistance from the tank sender goes from 10 ohm at full to 85 ohm at the top of the reserve line, and to 103 ohm at empty. So I'm thinking that an appropriate low fuel light would be about 90 ohm. I found a photo cell operated switch (the photo cell provides a changing resistance from dark to light) that can be set to trip at 90 ohm. I should be able to replace the factory circuit board with this device, using the fuel level resistance to replace the photocell resistance and regain low fuel light function. I've been playing around with this for a couple of years now (yes, not a priority in life) but if I get it to work I'll post more information on the modification. Quote Link to comment Share on other sites More sharing options...
pete3000 Posted December 5, 2021 Share Posted December 5, 2021 I found my td5 gauge converrsion had some messed up logic in the speedo, neither the temp gauge or fuel gauge worked correctly. I replaced the temp gauge with a vdo vision with matching 1/8 npt sender. The fuel gauge was adapted with the td5 gauge and a pcb gizmo called a gauge wizard. This is fully adjustable for any tank/sender/gauge and gives a low fuel light and a further flashing fuel indicator in lieu of a brown led. 🙂 Quote Link to comment Share on other sites More sharing options...
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