Member Jonathan Kay Posted July 19, 2015 Member Share Posted July 19, 2015 I see the logic, but I don't understand what's happening.As I understand it senders present a variable resistance to earth, often 10 to 160 ohm (don't know how much this varies between 7s) with a low resistance signalling a high pressure.So yours seems to be offering low resistance (high current blowing fuse, low resistance giving high pressure reading) soon after starting. So here's the question: is there no protection in the circuit for the sender shorting to earth? And if that's the case why is what you have observed so rare?Jonathan Link to comment Share on other sites More sharing options...
Macchiman Posted July 20, 2015 Author Share Posted July 20, 2015 Well, I spoke too soon! Went out for a test blat, ran for around 15 mins, then instrument fuse blown. Replace, and it ran for about 5 mins, blew, replaced, ran for another 5 mins and got me back home, fuse still OK. Left ticking over in drive for 15 mins, still OK. I think it's time to call an auto electrician......... Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 20, 2015 Member Share Posted July 20, 2015 Had you replaced the sender?I think it's getting close to removing the individual instrument feeds until you find out which is blowing the fuse...Jonathan Link to comment Share on other sites More sharing options...
Ian B Posted July 20, 2015 Share Posted July 20, 2015 Sorry haven't read the entire thread, but I would suggest the Oil Pressure sender is a red herring, as they would normally give a resistance to earth, with zero being full deflection (so shorting to earth will simply emulate that). I would suggest disconnecting the wire that goes to the speed sensor but at the point where it goes into the ECU. Link to comment Share on other sites More sharing options...
Macchiman Posted July 20, 2015 Author Share Posted July 20, 2015 Oil pressure sender is still disconnected.Ref the speed sensor, I'm at a bit of a loss trying to understand the wiring diagram, and don't feel that I could identify the correct wire and then disconnect it at the ECUShould I disconnect the variuos instruments behind the dash and/or at the senders?I think I've reached the point where I have to involve a specialist. Any pointers that I can pass on would be very useful.Thanks, Peter Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 20, 2015 Member Share Posted July 20, 2015 Ideas Rig a switched fused feed to the tacho. Remove the instrument fuse. See if the fault recurs. Disconnect the instrument feeds one by one. But that is awkward and time consuming, especially as the fault isn't immediate. And it won't check for faults (probably short to earth) in the wires upstream of where you disconnect them. So as far upstream as you can get. What Ian B says, or: Disconnect the speedo from the main harness. Have you got the diagram with the multiple connector for the dash near the top right and for the sensor near the bottom left? That should help you find it from the number and colour of the wires. If not would you like a copy?Jonathan Link to comment Share on other sites More sharing options...
Ray Pearce Posted July 20, 2015 Share Posted July 20, 2015 Have you considered something like http://www.ebay.co.uk/itm/Circuit-Breaker-Blade-Fuse-12V-24V-28V-Resettable-Marine-Rally-Car-Automotive-/391172924907 Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted July 20, 2015 Member Share Posted July 20, 2015 That's a very good idea, whether you only use them while you're sorting this out, or permanently.Are there any disadvantages? Can you get resettable ones that also light up when they're blown?Jonathan Link to comment Share on other sites More sharing options...
Martin J Posted July 21, 2015 Share Posted July 21, 2015 My mates car (sigma 150) had these symptoms & once towed to Mick Attrees he found a relay had overheated. Check all the relays. Perhaps just replace the one on the ignition circuit. They don't cost much.Good luck & keep us posted. Link to comment Share on other sites More sharing options...
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