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Unswitched / Unfused Live Wiring - Be Careful!


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I was just looking at tidying up some of the switches on my dashboard. It's always a good idea to disconnect the battery when working on the electrics but out of curiosity I had a look at the wiring diagram to see what was still live with the ignition switched off. What I noticed in particular was that some of the wiring to the dashboard switches was not only unswitched by completely unprotected by a fuse. I thought this was worth sharing just as a reminder / warning. The diagram below is for a K Series but others are probably similar. The yellow wires are live with the ignition off, but at least are fused. The red wires are connected directly to the battery without any form of short circuit protection. If you accidentally short of any these to ground with a tool while working on things you will in all probability do serious permanent damage to your wiring loom or even start a fire. On the dashboard these include the wiring to the lighting switch, flasher switch, ignition switch and immobiliser LED. Always disconnect the battery when working around potentially live electrics. Always disconnect the negative lead first and reconnect last (if your tools touch the bodywork whilst disconnecting the negative lead nothing will happen and once disconnected there is no return path if your tools touch the bodywork whilst disconnecting the positive lead).


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I could see your point if there were no fuse in the circuit, but there is ... it's just "downwind" of the switch wiring. When the headlamps are switched on, the headlights rocker switch activates a relay which switches power through to the main / dipped toggle switch. This sends it either via fuse 8 for main beam or fuse 9 for dipped beam to the lights themselves. I guess this at least means that the main and dipped beam are on different fuses so one won't take the other out.

Although it does surprise me that the dash switch wiring is unprotected against shorts, the main reason for my post was not to criticise the design but just to make people aware of the potential consequences of accidentally shorting the lighting switch wiring whilst working on the car. People may expect that the worst that would happen would be that a fuse somewhere would blow. In reality the consequences could be a burnt out loom and a lot of expensive wiring repair needed.



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  • 2 years later...

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