Battery Cut Off Switch
6 pole F.I.A master battery cut off switch isolates engine and protects alternator circuit against heavy voltage surge and prevents engine 'run-on'. Controls circuits up to 500 amps initial load with 100 amps continuous load 12 - 24v.
A properly fitted battery cut off switch makes a very good safety and security accessory. There are two ways in which it can be done, the first being the most simple and the second slightly more complicated and by far the better of the two.
The first is just to fit a basic isolator switch in the main +VE cable between the battery and the starter-motor common terminal (one of the leads will probably need extending so make sure you use the correctly rated cable, especially if you are extending the run). Mount the switch so it can be reached by the driver and remove the key whenever you park-up but DO NOT switch off the switch when the engine is running or you will damage the alternator.
The second way is to use a competition switch (pictured above) which incorporates two pairs of terminals as well as the main battery lead terminals. One of these pairs of contacts opens when you turn off the switch and kills the engine by either interrupting the ignition supply (petrol) or closing the fuel solenoid (diesel). The second pair of contacts closes when the switch is turned off and this diverts the power from the alternator (which is still producing power until it stops turning) and diverts this power through a ballast resistor to earth thereby protecting the alternator.
If you have accessories which require a permanent feed (radio, alarm etc) you can run an aux fuse box direct from the battery to power these items.
Both these switches are available from car accessory shops, motor-factors, race/rally specialists etc, the basic one is about £10 and the competition one is about £22 (both include 1 key but spares are only about £1 to buy). Some online suppliers include the following
rallylane.com (cheapest at less than £20 including VAT and postage)
On my Defender the switch is flush mounted in the passenger side of the seatbox just to the LH side of the tunnel. In this location it is out of the way yet within easy reach of the driver even when strapped in. The connections are made from underneath the vehicle and although access is a bit of a squeeze, when everything is connected up you will have no reason to go there again (maybe disconnect & clean the terminals every couple of years or so). Also locating the switch here means you can intercept the existing battery lead, cut it back & re-crimp and then just run a new one across to the battery which is only a very short distance away. I must admit I always upgrade the battery-lead but if you are not extending the run then the standard cable will be fine. The switch comes with instructions on how to connect it up but for the engine stop just intercept the fuel solanoid wire as this will do the job perfectly (it is actually the only way to stop a diesel).
This job is well worth doing and should only take a couple of hours as long as you have the new battery lead made up ready or can get one made up when you have actually started the work and know exactly how long it needs to be.
Options
Related Pages:
Back:
Return to Modifications page