Post
by Roy748 » Wed Jun 20, 2018 7:12 pm
Hello.
In most cases a blowing fuse is due to a short in the circuit somewhere, in that the live is shorting out with the earth.
If you trace the 3 wires from the switch you should find one going to earth one coming from a live source which from the sounds of it is the head lamp wire and the other, which will be live coming out of the switch when turned on, going to the fog light. Firstly trace all wires and look for any damage in the cable which could cause a short.
If you have a volt meter you can check the live supply is first going to the switch by removing the wire from the head lights that goes to the switch and placing the red volts meter probe to this wire and the black volt meter probe to a good earth such as a bolt attached to the bobywork. With your lights turned on you should get a current showing on the volts meter.
Next reconnect the head light wire to the switch and then disconnect the live wire which goes to the fog light, turn on your lights and then turn on the fog light switch. You should again see a reading on the volts meter. If not then the switch is faulty.
Finally if both the above show a reading of around 12V you need to disconnect the live wire at the fog light and again check with your lights on and the fog light switch turned on to check the supply isxreaching the fog light, again you shoukd a have a reading of around 12V.
If you do then it's the fog light itself which is at fault, which could be a bad earth connection or corrosion on the electrical connectors.
If you dont have a volts meter Try running a new live to the switch, ie remove the live supply wire coming from the head lamp.
Safest way to do this is to run a wire with an inline 5amp fuse fitted directly from the positive terminal on the battery to the switch. Remove the wire that feeds the fog light. As you want to isolate the switch at this stage.
Turn on the switch, If it blows the fuse again it's possibly the the switch at fault. If it does not blow the fuse connect a new piece of 5amp wire from the switch to the fog light live wire and test again.
This process just cuts out each length of existing wire with a new one which should help to identify if its a wire fault.
I should say first mind, check your earth wire from the switch and fog light are in good condition and have a good clean connection to a metal part of the body.
Looking at the switch photo you seem to have two wires going to one pin, each wire should have its own pin, live in, (turn switch on) live out and an earth wire pin.
Hope that helps
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