Ron4x4 Posted March 23, 2017 Share Posted March 23, 2017 On my Defender Ninety V8 from 1986 I noticed that the original PRC 3107 fuel gauge read "full" at all occasions. I have an STC1139 sender in my tank, originally used for diesel. This seems to be an often occurring issue. In order to solve the issue I found out that the STC1139 sender has a resistance range of 15 - 300 ohm ( full to empty) whilst the fuel gauge operates with a resistance range of 15 - 2000 ohm. Hence the little movement of the fuel indicator. How to solve this? Simple. The STC 3107 is made out of 5 sections, this is full - 3/4 - 1/2 - 1/8 and empty. See the red dots. First, cut through the resistor wiring using a Dremel grinder disk, at the position of the green lines. This is just above the red dot connector points. Then connect the red dots using 4 resistors, as indicated. Glue the resistors to the housing using 2-component epoxy glue which is resistant to fuel to avoid them coming loose. You will now see that the gauge reads in 4 sections: full, 1/2, 1/8 (indicator lamps jumps on) and empty, rather than on a gliding scale from full to empty. In practice however this reading is sufficient. Hope this is helpful! STC1139-done.pdfSTC1139-done.pdf 1 Quote Link to comment Share on other sites More sharing options...
Ron4x4 Posted March 27, 2017 Author Share Posted March 27, 2017 I see that I could not upload the picture explaining all this. Here is a description: use the following resistors in order to bridge the 0 - 2000 ohm: Full - 3/4 = 330 ohm; 3/4 - 1/2 = 330 ohm; 1/2 - 1/4 = 330 ohm; 1/4 - 1/8 = 330 ohm; 1/8 - empty = 680 ohm. You can skip the 3/4 indication by using 680 ohm between the top connector and the second position from above. The needle stays at FULL till it reaches the second dot position and then gets 680 ohm, jumping to position 1/2. And so on. The cutting should be done in the variable wiring section, just above these connector points; this way you create 5 (or 4) sections that should be bridged with resistors. Good luck. Quote Link to comment Share on other sites More sharing options...
Mo Murphy Posted March 27, 2017 Share Posted March 27, 2017 Good tech Ron, real garage landrovering. Mo Quote Link to comment Share on other sites More sharing options...
Ron4x4 Posted October 17, 2017 Author Share Posted October 17, 2017 I found an even easier solution to tackle this problem, and I should have thought about that earlier. It appears that the gauge receives a too high current which should be lowered by a resistor. Use a variable resistor between the blue/green sender connector at the fuel tank and any 12V wire to initially calibrate the gauge. Then replace by a fixed one in the dash. So, on the back of the PRC3107/PRC7313 gauge, just bridge the 12V terminal and the blue/green wire terminal, in my case this was a 127 ohm resistor. Problem solved. Quote Link to comment Share on other sites More sharing options...
bushwhacker Posted December 13, 2022 Share Posted December 13, 2022 Sorry to drag this up. But does anyone no for sure if this is a fix for the 110/90 fuel gauges, and is it as simple as the last post suggests or am I missing something? Regards Mark. Quote Link to comment Share on other sites More sharing options...
bushwhacker Posted December 14, 2022 Share Posted December 14, 2022 Anyone able to shed any light on this? Quote Link to comment Share on other sites More sharing options...
Troll Hunter Posted December 15, 2022 Share Posted December 15, 2022 I recently had indicating problems with my fuel gauge and it all came down to ensuring good earths, both at the sender and at the gauge. Problem solved. Mike Quote Link to comment Share on other sites More sharing options...
bushwhacker Posted December 22, 2022 Share Posted December 22, 2022 Thanks, funny how these sort of faults happy even when you are parked up then jump back in and see it! I really do not know how people live now with all the tech in vehicles now. Are we better of with it? Regards Mark. Quote Link to comment Share on other sites More sharing options...
Peaklander Posted December 22, 2022 Share Posted December 22, 2022 There is an earth post that affects the gauges - well it did on mine. It's on the transfer box and you can see it from the front, looking back along the right side of the vehicle (left as you look). Quote Link to comment Share on other sites More sharing options...
bushwhacker Posted December 22, 2022 Share Posted December 22, 2022 It is only minor fault but I do appreciate the suggestions to follow up, I have started a written list and will go at it again over the holiday period. Best wishes to everyone at this time. Mark Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.