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Horn working (sometimes)

Martin V

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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.

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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?

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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....

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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! :lol:

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!



Edited by dougbgt6
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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😬 

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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

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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.

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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 !!!


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