Martin V Posted July 18, 2023 Report Share Posted July 18, 2023 GT6 MK3 1973 (new wiring loom fitted by prev owner on car restoration) Any ideas why my horn might work without ignition on but not work when ignition is on ? Is it the relay? or incorrect wiring to relay? There is one wire connected to top terminal (C1), two wires connected to middle (C2) and one wire to lower terminal (W1). Many thanks. Link to comment Share on other sites More sharing options...
johny Posted July 18, 2023 Report Share Posted July 18, 2023 Looking at the wiring diagram in the free to download workshop manual it should be a purple/yellow onto C1, 2x purple onto C2 and a purple/black onto W1. However I dont think this is going to solve the problem as one of the purple wires is the power supply to the relay and this should be permanently live and also supply the hazard lights via the other purple wire. The question is do these work as they should with with the ignition off? Link to comment Share on other sites More sharing options...
dougbgt6 Posted July 18, 2023 Report Share Posted July 18, 2023 This is how it should be wired, off the "top fuse" (which is not always the top fuse!) WHICH then attaches to the ignition switch. I suspect this is where the incorrect connection lies.4 Doug Link to comment Share on other sites More sharing options...
Martin V Posted July 18, 2023 Author Report Share Posted July 18, 2023 Thanks Johny, Doug . I will investigate further. Thanks very much for the wiring diagram, so much clearer than my manual. I also hadn’t seen a free manual download which I’ll now find. cheers Link to comment Share on other sites More sharing options...
Graham C Posted July 18, 2023 Report Share Posted July 18, 2023 Have an earth wire on the steering knuckle, as below? Graham Link to comment Share on other sites More sharing options...
Martin V Posted July 19, 2023 Author Report Share Posted July 19, 2023 Thanks Graham, it does seem to have the strap. I’ll check it is functional. Should there be an earth from the steering rack grease plug? On some workshop pics I’d seen one but not in mk3 parts catalogue. Link to comment Share on other sites More sharing options...
johny Posted July 19, 2023 Report Share Posted July 19, 2023 there certainly has to be some method of earthing the steering column for the horn to work and the connection from rack grease plug to chassis is the usual one... Link to comment Share on other sites More sharing options...
Martin V Posted July 19, 2023 Author Report Share Posted July 19, 2023 Thanks Johny. Will add as this was originally also pointed out by friend. Link to comment Share on other sites More sharing options...
johny Posted July 19, 2023 Report Share Posted July 19, 2023 Let us know what you find with the ignition only horn problem.... Link to comment Share on other sites More sharing options...
johny Posted July 19, 2023 Report Share Posted July 19, 2023 15 hours ago, dougbgt6 said: Like the diagram Doug. Minor thing is the interior lights connections - looking at the manual I think both the lights (roof and ignition key) are illuminated by all the switches (boot, dash and both door switches) so I think theres a little connection dot missing from the purple/white wires in the drawing.... Link to comment Share on other sites More sharing options...
Colin Lindsay Posted July 19, 2023 Report Share Posted July 19, 2023 If the horn works at all then I suspect as Doug says the problem is at the ignition switch. The live feed is possibly taken from the wrong switch terminal? Link to comment Share on other sites More sharing options...
dougbgt6 Posted July 19, 2023 Report Share Posted July 19, 2023 (edited) Guys, The diagram is from this site: Wiring Schematics and Diagrams - Triumph Spitfire, GT6, Herald I downloaded it and got my daughter to laminate it. There's a guy on FleaBay selling laminated circuit diagrams, £15! Diagram errors! Dots: What Johny describe is the way it works and what I deduce from the diagram. Although expecting it to work the way I think it should makes me think the diagram says that! The fuses are misnamed, the purple fuse is not top, the green not middle and the red not bottom, at least they weren't on my car, But remembering them as colours rather than positions works, as long as you've figured out where they are! I now have a 10 blade fuse box which was easy to install, took the 4 purple wires off the fuse and relocate them to the blade box. The red fuse appears to have 2 connections and a branch off the dash illumination to the side lights. Actually the side lights go to the fuse and the red fuse has 3 connections. Similarly the green fuse appears to have 3 connections, but reality it's 4. So 3+3+4 neatly makes 10! Simples. All a matter of misplaced dots! Beware the Spitfire diagram, the site is American and American Spitfires have extra bits! Doug Edited July 19, 2023 by dougbgt6 1 Link to comment Share on other sites More sharing options...
Martin V Posted July 19, 2023 Author Report Share Posted July 19, 2023 HI, Initial checks show that the warning lights work with ignition on and off. Horn works only with ignition off. looks like it is the topic as per ignition feed - now to get to see that and understand it. Link to comment Share on other sites More sharing options...
johny Posted July 19, 2023 Report Share Posted July 19, 2023 That is strange as it should be the same supply for the horns as the hazard lights and the most likely possibility was that the purple feed wire was connected to the ignition powered fuse (should only have green outgoing connections) instead of the battery powered one. Now its more of a mystery😬 Link to comment Share on other sites More sharing options...
dougbgt6 Posted July 19, 2023 Report Share Posted July 19, 2023 This was on 'ere 2021 might be helpful, or confusing! Doug Link to comment Share on other sites More sharing options...
johny Posted July 19, 2023 Report Share Posted July 19, 2023 But the horn/hazard supply shouldnt go anywhere near the ignition switch should it? Link to comment Share on other sites More sharing options...
johny Posted July 19, 2023 Report Share Posted July 19, 2023 Martin, it might be helpful to test all the cars electrical components, one by one, to see if they operate with ignition on and off and if theres any anomalies. It could make it much easier to find where the problem is.... Link to comment Share on other sites More sharing options...
Martin V Posted July 19, 2023 Author Report Share Posted July 19, 2023 1 hour ago, johny said: Martin, it might be helpful to test all the cars electrical components, one by one, to see if they operate with ignition on and off and if theres any anomalies. It could make it much easier to find where the problem is.... LOL to a complete novice this will probably make my head explode 🙂 but yes makes good sense Link to comment Share on other sites More sharing options...
Martin V Posted July 24, 2023 Author Report Share Posted July 24, 2023 Solved, not by myself I must add. Many thanks to Grace for multiple diagnostics. Solution was back to Johny’s comment that I needed the earth from Rack to Earth. The strap across the joint was there but guy who rebuilt it didn’t refit an earth from column The horn could work when ignition not on because the steering lock engages the column and provided the earth it needed to work. Ignition on meant that the earth it was hijacking was no longer present. Fitted a short earth between rack grease nipple and one of bolts holding coolant expansion bottle. Working with and without ignition on. Thanks again for your hints and excellent wiring diagram being shared. Everything else working fine. 1 1 Link to comment Share on other sites More sharing options...
PeteH Posted July 25, 2023 Report Share Posted July 25, 2023 I wouldn’t beat yourself up about it. Many an experienced mechanic has missed an earthing issue. Old vehicles can be notorious for bad/poor/missing earth returns. Pete Link to comment Share on other sites More sharing options...
Martin V Posted July 25, 2023 Author Report Share Posted July 25, 2023 Thanks Pete. I’m learning quickly and finding these errors made by the guy who put it together. Link to comment Share on other sites More sharing options...
johny Posted July 25, 2023 Report Share Posted July 25, 2023 All part of the fun🤔 Link to comment Share on other sites More sharing options...
Pete Lewis Posted July 25, 2023 Report Share Posted July 25, 2023 5 hours ago, Martin V said: guy who put it together trying to un fathom previous owners logic can take much longer than you think more strong tea and some cursing can help with a what the .......and why ... is quite common headache material of new ownership but after 20 years thing start to improve Ha !!! Pete Link to comment Share on other sites More sharing options...
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