The Frozen North Posted November 5, 2022 Share Posted November 5, 2022 Good evening all.Just got my Seven back after an unfortunate incident involving a sharp corner and an armco barrier on a bridge. It certainly looks a lot better than when I last saw it but I now have an issue with the fuel guage system. The fuel guage reads super high and does not respond to the fuel tank level.The resistance across the sender unit goes from 263 ohms with the float fully down / empty to 22 ohms float fully up / full.With the sender unit disconnected the voltage across the sender input wire and earth with the ignition on is 0.13V.My presumption is that the issue is with the wiring between the sender and the guage. I have tried running a test wire from the guage to the sender but in fairness I am not sure what I am doing at the guage end.Any advice gratefully received.Thank you. James Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted November 5, 2022 Member Share Posted November 5, 2022 I'll send you the wiring diagram if you give me your email address in a Private Message.For a 1996 K that's a point to point diagram which makes it easy to check everything with a test jump wire as you've tried.Jonathan Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted November 5, 2022 Member Share Posted November 5, 2022 It does sound like a wiring problem, especially with that history of trauma.Have you exposed the connections at the tank end?Are all of the other instruments working correctly?As the gauge is reading high it's getting an earth from somewhere. You'll probably have to access the connections on the back of the gauge at some point.Jonathan Link to comment Share on other sites More sharing options...
The Frozen North Posted November 5, 2022 Author Share Posted November 5, 2022 Hello Jonathan.I will send private message with email address shortly.I have the Caterham wiring diagrams but must confess when comes to the guage I am bit lost.All other instruments and lights working. I thought I had found a break in the supply wire at the tank end but bypassing that had no effect. The tank end was very much in the zone of damage as a new tank and rear basket was needed.James Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted November 5, 2022 Member Share Posted November 5, 2022 Thanks.Your post crossed with some changes that I made to #3.Jonathan Link to comment Share on other sites More sharing options...
The Frozen North Posted November 5, 2022 Author Share Posted November 5, 2022 Thank you. Connections exposed at tank end and sender unit currently out of the tank so I can play with it.As mentioned in my PM I did find a break near the tank but bypassing that has not resolved the issue.Will the sender wire run continuously to the guage or is there another point / connector to test before the guage?If I run a test wire is it simply a case of running the wire from the appropriate lead on the guage to the input on the sender unit? I have tried this but not sure if I got the correct lead on the guage.James Link to comment Share on other sites More sharing options...
The Frozen North Posted November 5, 2022 Author Share Posted November 5, 2022 Thank you Jonathan.I will run a test wire from where green brown enters the guage directly to the sender and see what happens. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted November 5, 2022 Member Share Posted November 5, 2022 I that that it's Green/ Black from sender to gauge. Abbreviated to GB.And I wonder if the fault is that it is contacting earth somewhere other than through the sender. If that's the case then you need to disconnect it from the gauge in order to test anything else.The first thing that I would do is disconnect that wire from the sender at the tank end. What happens to the gauge reading?Jonathan Link to comment Share on other sites More sharing options...
The Frozen North Posted November 5, 2022 Author Share Posted November 5, 2022 Thank you re wiring colour.Disconnecting at the sender end does not change the gauge reading.Must confess to getting a bit confused with senders and resistance. My initial research suggested that max resistance = full tank so I inferred that my situation must mean break in the wire. Having now tested the sender and found max resistance= empty then as you infer the issue may be a short circuit.Would all Caterham senders of this age have been max resistance = empty?JamesPS Just found your archived post from 2.3.17 re fuel gauge wiring with a photo of what looks like my gauge. Link to comment Share on other sites More sharing options...
The Frozen North Posted November 5, 2022 Author Share Posted November 5, 2022 Link to photo of fuel guage connectors + wiring key:https://www.pistonheads.com/gassing/topic.asp?t=1283314 Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted November 5, 2022 Member Share Posted November 5, 2022 I'm now not sure what's happening. Let's assume that your resistance readings from the sender show which way it's supposed to work in your Seven. I'm sorry if I've caused confusion.How about trying that test jump lead and seeing how the gauge responds?Jonathan Link to comment Share on other sites More sharing options...
The Frozen North Posted November 6, 2022 Author Share Posted November 6, 2022 After a bit of fumbling in the garage and extended yoga in the front passenger footwell a short circuit has been confirmed as the issue.A big THANK YOU to Jonathan Kay for his help. Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted November 6, 2022 Member Share Posted November 6, 2022 : - )Well done.Jonathan Link to comment Share on other sites More sharing options...
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