walliver Posted June 5 Share Posted June 5 (edited) Hi all I have a 2012 sigma Academy race car which is a new car to me and I'm trying to get it through an MOT next week. I connected the rear and front lights and replaced the flasher unit, which resulted in lights and hazards, indicators all working as they should. Nice and simple... pretty pleased...however now it won't start (it turns over slowly and doesn't fire). It also smells hot behind the dashboard when I turn the ignition on, more so when I crank the engine... So I've taken the scuttle off and the black ground wires behind the lights, indicator relays and flasher unit are heating up enough to melt the insulation in small localised places. Same goes for the white wire from the indicator relay (as per the 2014 assembly guide wiring diagram). No fuses are blown (I've taken out the fuses for lights and indicators, heater, heated screen (according to the wiring diagram) because i thought that would isolate the issue a bit (it is still happening with fuses removed). Fuel pump primes OK (it is directly wired from the FIA cut out switch to the pump I think). The battery is healthy and trickle charged. It has an FIA cut off switch and starter button. I am assuming something is shorting to ground and powering up the earth circuit, taking current from the starter circuit and dumping the energy into the ground circuit. But I'm not sure how to test where this is happening or which circuit it is happening in. I'm not an electrician so be grateful for advice on how to diagnose the issue/things to check and find the short? Thought I'd try the wisdom of BC before calling an auto electrician. Thanks for reading this far! cheers Edited June 5 by walliver Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 5 Member Share Posted June 5 5 minutes ago, walliver said: ... as per the 2014 assembly guide wiring diagram... There are at least three different layouts of relays and fuses on Sigma-engined Sevens. I'd check what you've got against the layout in the Owner's Handbook as well as the wiring diagram in the Assembly Guide. If they don't match your Seven please let us know what you've actually got and we'll find the matching layout. Jonathan 1 Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 5 Member Share Posted June 5 24 minutes ago, walliver said: ... however now it won't start (it turns over slowly and doesn't fire). It also smells hot behind the dashboard when I turn the ignition on, more so when I crank the engine... EDITED: I suggest disconnecting the battery whenever you're not working on the car until this is sorted. ... What's the battery voltage with the ignition switch OFF, then with the ignition switch ON, and the minimum seen as it cranks on the starter? Jonathan Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted June 5 Share Posted June 5 I think the problem is more likely to be a bad or broken ground between the engine or starter motor and the chassis, resulting in alternate paths being found back to the battery. If you don't have less than 0.2Ω between the engine and starter motor and the battery negative, I would resolve that as a problem before looking for other issues. 1 Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 5 Member Share Posted June 5 4 minutes ago, aerobod - near CYYC said: I think the problem is more likely to be a bad or broken ground between the engine or starter motor and the chassis, resulting in alternate paths being found back to the battery. If you don't have less than 0.2Ω between the engine and starter motor and the battery negative, I would resolve that as a problem before looking for other issues. Do you need to disconnect or switch off anything before measuring that resistance? Thanks Jonathan Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted June 5 Share Posted June 5 (edited) 4 minutes ago, Jonathan Kay said: Do you need to disconnect or switch off anything before measuring that resistance? Thanks Jonathan Hi Jonathan, To eliminate any stray current if there is a short that could give a false reading, I would disconnect the battery +ve terminal first. Edited June 5 by aerobod - near CYYC Link to comment Share on other sites More sharing options...
Member Jonathan Kay Posted June 5 Member Share Posted June 5 4 minutes ago, aerobod - near CYYC said: To eliminate any stray current if there is a short that could give a false reading, I would disconnect the battery +ve terminal first. Thankyou Jonathan Link to comment Share on other sites More sharing options...
walliver Posted June 6 Author Share Posted June 6 Thanks both, much appreciated. Battery is disconnected 🙂 - I will take battery readings and see if I can measure resistance later today. The wiring diagram is good except for the hazards wiring which is different. Because they worked though, this may be a red herring. I will check the fuse layout in the owners manual too. Thank you. Link to comment Share on other sites More sharing options...
SM25T Posted June 6 Share Posted June 6 Agree with above that problem is a missing earth from engine to chassis. Do disconnect battery until resolved. You don't want an electrical fire under the dash Link to comment Share on other sites More sharing options...
walliver Posted June 6 Author Share Posted June 6 Update on readings after I have cleaned the earths on the dashboard (on the wiper plate), the engine mount to chassis, the bell housing, and the lights. I read 0.2ohms between battery negative and starter and engine block. Battery reads 12.7v standalone and connected, but I don't want to crank it really. Unfortunately I still get the same issue when I turn on the ignition, will carry on troubleshooting Link to comment Share on other sites More sharing options...
aerobod - near CYYC Posted June 6 Share Posted June 6 2 minutes ago, walliver said: Update on readings after I have cleaned the earths on the dashboard (on the wiper plate), the engine mount to chassis, the bell housing, and the lights. I read 0.2ohms between battery negative and starter and engine block. Battery reads 12.7v standalone and connected, but I don't want to crank it really. Unfortunately I still get the same issue when I turn on the ignition, will carry on troubleshooting If you disconnect all earths on the dashboard grounding post(s), do you still get 0.2Ω between the battery negative and starter and engine block? Link to comment Share on other sites More sharing options...
walliver Posted June 6 Author Share Posted June 6 (edited) 57 minutes ago, aerobod - near CYYC said: If you disconnect all earths on the dashboard grounding post(s), do you still get 0.2Ω between the battery negative and starter and engine block? Thanks for the suggestion - yes the readings are the same, and stable Edited June 6 by walliver Link to comment Share on other sites More sharing options...
jbcollier Posted June 7 Share Posted June 7 Take a high wattage headlight bulb and attach two wires with alligator clips at the ends so high beam is illuminated when it is hooked up to a battery. Disconnect the negative battery cable at the battery and hook up your new test light between the cable and the negative terminal of the battery. Turn on whatever is causing your short. If it is shorted, the bulb will glow brightly but the bulb will restrict current enough so nothing is damaged. Now you can start pulling fuses or disconnecting wires/components until the bulb dims. You have found your short. If the short is on a specific circuit, then remove that fuse and hook up the test light across the fuse. Now you can pry and poke about that circuit without constantly blowing fuses. When the light dims, you’ve found your short. 2 Link to comment Share on other sites More sharing options...
Colin_T Posted June 7 Share Posted June 7 Do you get any issues when not trying to crank the engine ? I.e is wiring getting hot even with just the ignition on? if it’s just when cranking > check engine earths. As a quick test you can even make a temporary one up with a jump lead from a gearbox bolt direct to negative terminal and see if it then cranks and starts fine. it will try and earth anyway it can, I’ve seen melted throttle cables where it’s tried to use the throttle cable as an earth path. Link to comment Share on other sites More sharing options...
walliver Posted June 7 Author Share Posted June 7 3 hours ago, Colin_T said: Do you get any issues when not trying to crank the engine ? I.e is wiring getting hot even with just the ignition on? if it’s just when cranking > check engine earths. As a quick test you can even make a temporary one up with a jump lead from a gearbox bolt direct to negative terminal and see if it then cranks and starts fine. it will try and earth anyway it can, I’ve seen melted throttle cables where it’s tried to use the throttle cable as an earth pat Thanks for the replies everyone. Wow, melted throttle cables! Yes it's getting hot with just the ignition on unfortunately. I'm hoping to do some more investigation this weekend and track down the problem circuit. It seems isolated to the earth across the relays for lights and hazards (the supplies to activate the relays, as opposed to the circuits activated by the relays if I have understood things correctly)... But the earths all go into a bundle linked to the buzzer so I'm planning to check resistance across all circuits connected to that bundle. Didn't expect to get to know the wiring of a sigma so intimately I must admit! Link to comment Share on other sites More sharing options...
walliver Posted June 8 Author Share Posted June 8 Thanks for your help so far. I may be missing something really obvious... but from some very basic investigation, I've found that; - If I remove the fuel pump relay, the issue goes away. The car tries to start and splutters before it runs out of fuel: there are no melting wires behind flasher unit or indicator relay when I turn on the ignition. - when connected the fuel pump does prime. - the lights and hazards, indicators all function correctly despite being the subject of the melted wires. - no fuses are being blown - Current battery readings are 10.8v cranking (without fuel pump) and 12.6V ignition on, 12.6V ignition off. - reading 0.2 ohms between battery negative and dashboard, block and starter earths. Also reading 0.2 ohms between fuel pump ground wire and chassis. I admit I am confused why the earth behind the flasher unit and the indicator relay are melting when it appears it's the fuel pump relay / circuit with the issue? I've found some amazing articles on BC but it's beyond my bandwidth/ability. I do appreciate v hard to help via a forum!! but any suggestions welcome. Hopefully this is obvious to someone other than me! 🙃 Link to comment Share on other sites More sharing options...
CAT170 Posted June 8 Share Posted June 8 I'm not an expert with electrics but could the fuel pump relay be the culprit? Or the wiring on the fuse box behind the relay? Link to comment Share on other sites More sharing options...
walliver Posted June 9 Author Share Posted June 9 Thanks, I've tried the fuel pump relay in the hazards circuit and it works fine, it I don't think that's it. Looking at the wiring behind the fuel pump relay: - green is switched ignition which reads 12.5v. supplies other relays which are working fine - black earths to dash with 0.2ohms resistance - brown live reads 12.5v - black orange to chassis loom looks ok from what I can see. Connects through to chassis - fuse wires look good, connect to the connector at the tank ok. Still not sure why the ground wires are heating up - perhaps I'm not testing the correct thing and the fuel pump relay is a red herring! Link to comment Share on other sites More sharing options...
raw Posted June 9 Share Posted June 9 Little bit curious as why there is a black wire to earth on the fuel pump relay? Green is switched ignition supply to the relay coil which is energised by the ecu via the black/orange (ECU switches to earth). Brown is the main power feed from the battery (often from the starter motor eyelet). There should be a yellow/green wire to a fuse with a second green/yellow wire from the fuse to the inertia switch and then off to the fuel pump - do Academy cars have the inertia switch or is it bypassed? The black wire should not be connected to ground otherwise all that is happening is that the fuel pump relay is connecting the battery direct to ground! Hope this gives you a few more pointers? Cheers Andrew Link to comment Share on other sites More sharing options...
Colin_T Posted June 9 Share Posted June 9 With the black wire disconnected from ground, check to see if there’s a voltage present on the wire ?? Your ecu should be earth for the relay, as the ecu switches grounds to complete the relay coil circuit. So maybe check your ecu grounds are good and clean. Are they direct to the battery? Link to comment Share on other sites More sharing options...
walliver Posted June 9 Author Share Posted June 9 Thanks all, really helpful and has given me some more things to check and I've found contrary to the wiring diagram: The fuel pump relay is wired to earth instead of the yellow green feed to the fuel pump fuse N. The YG from fuel pump relay to fuse N is missing. The fuel pump fuse N is wired to earth on one terminal (instead of the feed from the relay) and yellow green wire to the fuel pump on the other. The "ignition supply engine" fuse S is wired to earth on the same terminal as the white and orange wire. Race car things done while the immobiliser was removed? It ran fine previously so it must work... Link to comment Share on other sites More sharing options...
walliver Posted June 9 Author Share Posted June 9 1 hour ago, Colin_T said: With the black wire disconnected from ground, check to see if there’s a voltage present on the wire ?? Your ecu should be earth for the relay, as the ecu switches grounds to complete the relay coil circuit. So maybe check your ecu grounds are good and clean. Are they direct to the battery? Just to add...I couldn't measure any voltage on the black wire when disconnected from ground. The ECU grounds are to a post on the bulkhead which is clean, and the issue remains when connecting direct to battery 🙂 Link to comment Share on other sites More sharing options...
Colin_T Posted June 9 Share Posted June 9 Any difference if you Disconnect the plug off the fuel pump itself ? Link to comment Share on other sites More sharing options...
raw Posted June 13 Share Posted June 13 I had another think about this and also worked on a similar car this week. The black wire from the fuel pump relay should not be connected to earth because when the relay is powered up by the ignition/ecu, it is switching 12V directly to ground in its current wired form. The black wire that goes to Fuse N should also not be connected to earth. Disconnect both of these wires from the earth and join together. Your fuel pump relay should then work as designed. Cheers Andrew 1 1 Link to comment Share on other sites More sharing options...
walliver Posted July 3 Author Share Posted July 3 (edited) Belated thanks for the help on this. Andrew - your solution was spot on, rewiring as you described solved the problem and has since been checked over: all good. Thanks. No idea why it was wired as it was - it would have been like that for majority of it's racing life! Anyway, thanks again all. All MOT'd now and enjoying a few road drives before getting it back on circuit. Cheers! Edited July 3 by walliver 2 Link to comment Share on other sites More sharing options...
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