Troll Hunter Posted November 1, 2012 Share Posted November 1, 2012 Hi, All, Please can someone give me help on the above? The vehicle is a '91 V8 110CSW, later fitted with a 300Tdi, but all the wiring is basically original. My fuel gauge used to work normally, allowing for the usual Land Rover error band, but now permanently shows Full, and my Low Fuel warning light is permanently on. Why? Should the fuel gauge, when disconnected from both electrical connections, show eletrical continuity between the two terminals when tested with a multi-meter set on Ohms? If so, what resistance should it have? I've just bought a new fuel tank sender unit, original type, which has three electrical connections on it, which are horizontally next to each other when the sender is installed. The wiring diagram in the LR manual, see attachment, shows three connections, but earlier wiring repairs/modifications have rendered wiring colours meaningless. Item 70 is the fuel gauge and item 81 is the sender unit. Which wire from the instrument panel goes to which sender connection? Any help will be very much appreciated. Wiring Diagram.pdf Quote Link to comment Share on other sites More sharing options...
pete3000 Posted November 1, 2012 Share Posted November 1, 2012 Only one wire goes back to the gauge, the other two, one ground (black) and a feed from +12v to sender from your diagram it looks like it is perm live, though I would take that with a pinch of salt. Shoukd be switched live The ground should be obvious if it looks like a tack welded lug onto sender body (not insulated) then try swapping the other two round. found this link for 90 tank, http://forums.lr4x4....showtopic=19112 Quote Link to comment Share on other sites More sharing options...
western Posted November 1, 2012 Share Posted November 1, 2012 green/black to sender unit forward spade terminal -- feeds the fuel gauge plain black to ridged stud sender earth white/slate to sender unit rear spade terminal -- feeds low fuel warning light. Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted November 1, 2012 Author Share Posted November 1, 2012 Pete3000 and Western, Many thanks for the link and info. I've identified which wire is which, and now it all seems to be connected correctly, but I've not yet re-installed the sender unit, so I can move the float up and down to simulate a full or empty tank. And yes, the system is only live with the ignition ON. With the level gauge disconnected and with both the level gauge and the sender unit disconnected the low level warning light stays on at all float positions. How should I test the level gauge? I've opened the gauge - minor aesthetic damage only - and nothing appears to be amiss there, i.e. no loose wires evident, even under a magnifying glass, 'cos they're so damn fine. What value should the resistor be? It's 21 years old, and the colours are somewhat indistinct - no, I'm not colour blind - but the bands appear to indicate 680MOhm (Blue, Grey, Violet and Gold), which doesn't seem right. Do resistors deteriorate? Any help will be very much appreciated, please. Many thanks, Mike Quote Link to comment Share on other sites More sharing options...
western Posted November 1, 2012 Share Posted November 1, 2012 no idea about the resistor, I'm assuming it's inside the gauge ? I don't know of any other resistors in the fuel gauge wiring. Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted November 1, 2012 Author Share Posted November 1, 2012 Yes, it's inside the fuel gauge. Should there be electrical continuity across the fuel gauge terminals, and if so, what would the resistance be? Is the fact that the low fuel warning light is permanently ON a symptom of other electrical problems? Everything else appears to be working normally. Quote Link to comment Share on other sites More sharing options...
bodumatau Posted July 18, 2016 Share Posted July 18, 2016 a bit nerve wracking pushing 12V live through a full tank of fuel.... must admit I wasn't quite at ease..... my gauge has a number on it: PRC3107, the 12V feed only works connected one way around, so must be some sort of diode inside too.....looking at the back of the gauge the 12v goes onto the right side lug and the green/black wire to the tank on the LEFT lug. my sender unit didn't work with the earth at the bottom, had to be in the middle and now it seems to be working fine, lets see if it shows me as the tank empties.......lets see. Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted July 18, 2016 Share Posted July 18, 2016 EFI pumps sit immersed in PETROL not diesel, and they have nothing but normal crimp on spade connectors, and they will pull far more current than a gauge sender Quote Link to comment Share on other sites More sharing options...
bodumatau Posted July 20, 2016 Share Posted July 20, 2016 I KNOW!!!! almost sounds like an instruction manual to make a bomb....... "now you insert an electric motor running on 12V into 80 litres of highly flammable petrol"...... "then as redundancy connect your fuel gauge to 12V, just in case your fuel pump doesn't blow you up" and we drive around with these........ nerve wracking.... Quote Link to comment Share on other sites More sharing options...
stephencdavies Posted July 20, 2016 Share Posted July 20, 2016 Sticking a pump wired up to 12v into a tank of highly volatile liquid isnt for the faint of heart. my only tip would be, Not to do at night by candle light Quote Link to comment Share on other sites More sharing options...
bodumatau Posted August 3, 2016 Share Posted August 3, 2016 ok so now I have a new PRC7313 blue box gauge from a known supplier, fitted to the tank sender which is also a newish blue box and I am only getting reading between FULL and HALF...... any ideas what I am doing wrong? same for the older sender unit, also only shows from FULL to HALF. (at first I SUSPECTED it might be a 24V gauge but that is another part number.... PRC7314, so that rules that out.) Quote Link to comment Share on other sites More sharing options...
montyjn Posted August 3, 2016 Share Posted August 3, 2016 faulty gauge? Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted August 4, 2016 Author Share Posted August 4, 2016 I fitted a new sender unit, a B**tpart item, and it was faulty as delivered. What a surprise! Do your best to avoid their carp. I'm now ordering what I think is a Bearmach one, and hopefully it will work. Mike Quote Link to comment Share on other sites More sharing options...
bodumatau Posted August 5, 2016 Share Posted August 5, 2016 yep I have the bearmach one in, any way to test the gauge? Quote Link to comment Share on other sites More sharing options...
montyjn Posted August 8, 2016 Share Posted August 8, 2016 From memory you take the gauge out from the instrument cluster and take a direct feed from the battery, this should swing the gauge to full; meaning it works. Quote Link to comment Share on other sites More sharing options...
bodumatau Posted August 8, 2016 Share Posted August 8, 2016 yes that happens, 12V thru the gauge gives me full tank, then I plug it all in, move the sensor to full tank and get gauge saying full tank, then slowly take it down to empty and the gauge doesn't get less than half tank...... Quote Link to comment Share on other sites More sharing options...
montyjn Posted August 8, 2016 Share Posted August 8, 2016 Hmm. I'm a little stumped. I would guess the sender is faulty (issue with the contacts (their angle or breaks in the copper bands it runs on))? Although I appreciate it's occurring to both.. I don't think it would be an earth fault given you get a full reading (i.e. no resistance) when connected up. I assume the wiring for the low fuel light and gauge reading is the correct way round (low fuel light at the bottom)? Quote Link to comment Share on other sites More sharing options...
bodumatau Posted August 14, 2016 Share Posted August 14, 2016 doesn't look like the low fuel light gauge is connected, lug is there but no wires inside.... maybe I need to ask this question another way around, which sensor is the right sensor for gauge PRC7313? I suspect I might have the wrong sensor? only thing that makes sense, which would mean my old gauge is working fine just wrong sensor? Quote Link to comment Share on other sites More sharing options...
montyjn Posted August 15, 2016 Share Posted August 15, 2016 The fuel sender part number is dictated by the vehicle and fuel type. My 110 is a v8 carb (which I think yours was originally), so the part number would be STC 1482. Now yours is a diesel, I believe you could also use a different one (PRC 8463 or AMR 1495), but I am not sure they would have a low fuel level warning light though as the parts diagram (page 521) suggests they don't. I think the difference between petrol and diesel was the float (metal or plastic respectively), but perhaps someone with more knowledge could shed a little light.. Quote Link to comment Share on other sites More sharing options...
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