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Steve Q

Fitting a battery master switch

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Car security has come a long way in the last twenty years thanks to improved locks and immobilisers, however with the introduction of keyless entry and keyless ignitions car theft is sadly on the increase.

To help boost security you could look at fitting a battery master switch which acts as a type of immobiliser by cutting off the negative earth electrical supply but allows the alarm, radio and clock to function when the master switch is fitted with a fuse holder. If this sounds like a good idea to you, then my first piece of advice would be to assess where you are going to fit the switch. You’ll probably need to do measuring so in order you can buy/make brackets to hold the switch. To fit a battery master switch you’ll need:

1. Battery master switch, with key and fuse holder   Examples from eBay


2. Four gauge wire from an auto accessories/ICE shop


3. Four Ring terminals 


4. Suitable brackets


5. Nuts and bolts. This will depend on the size of brackets you’ve bought/made and where you have placed them.



Step 1

Disconnect the battery. This might seem obvious but if you forget you run the risk of running the cars electrical system through you! 


Step 2

Assuming you have decided on where you’ll fit the switch, the next job is to attach your brackets through the holes in the switch base.


Step 3

Attach the ring terminals to the four gauge wire.


Step 4

Break into the battery negative lead and attach the four gauge wire with ring terminals. It might be worth crimping it to hold it in place as well.


Step 5

Connect the negative battery lead to one of the master switch connectors and use a ring terminal to connect the fuse holder.

Step 6

Connect the other end of the fuse holder to the switch and then re-join the four gauge wiring to the battery. 


Step 7

If you haven’t done already, attach the switch and its brackets to your chosen part of the vehicle.

Step 8

Then fit the fuse into the fuse holder. Your fuse and fuse holder may differ from the one shown in the picture. 


Step 9

Test your handy work by fitting the red key and starting the ignition. If all is well then take the red key out and job done. Just don’t lose red the key!

Picture below showing an example of the finished article. 


Please note that the items shown in the pictures may differ from the one available in your country, however the fitting process will be the same.

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