Posted on: November 18, 2015

by Stu Brennan in the March 1996 RootesReview

You can shut off power to most of your Sunbeam’s electrical circuit with the ignition switch. But, there is still quite a lot of +12V in parts of the wiring harness, including portions unprotected by fuses. When my Tiger isn’t going to be used for an extended period, I like to disconnect the battery, just in case a short develops. We have heard stories of mice nibbling on wires, etc. However, access to the Tiger’s battery requires that the trunk first be emptied. Two quarter turn fasteners must then be released with a large screwdriver. Upon lifting the false trunk floor, access to the battery is finally gained. Needless to say, this doesn’t get done every night.

A short on the road is much more likely, since everything is being wiggled about. Imagine trying the above drill while in a panic at the side of the road.

With my wiring harness approaching its 29th birthday, I decided to install a battery shutoff switch. Walmart supplied the 300 Amp switch for about $9.00, though fancier versions can cost up to 4 times more. The switch was mounted in the rear facing side of the battery plateau in the false trunk floor. Here, it’s easy to reach, and relatively safe from sliding tool boxes (A “U” shaped cabinet handle was added to fully protect it). Other locations are possible. I briefly considered ways to make it accessible from the driver’s seat.

The switch was located in the ground lead of the battery, so that modification of the heavy +12V cable, that carries power forward, would not be required. An added safety benefit is that all of the new wiring, and the exposed terminals on the switch, are at ground potential. Most auto parts stores carry a variety of lengths of replacement battery and starter cables, eliminating the need to cut or splice any of the high current wires.

For an extra layer of insulation, all of the new wiring, and the portion of the 12V cable in the trunk, was covered with “Split Loom”, that ribbed plastic tubing that is slit up the side. The only permanent modification required was the hole in the wood trunk floor, which could be easily filled and covered.

So now, I can just open the trunk and give the switch a quarter turn, and know that all power is shut off. With the key removed from the black switch body, the exposed portion isn’t very noticeable, so it also could be a bit of a theft deterrent, even if the weasel managed to open the trunk. Granted, anyone who knows Tigers could figure it out in a few seconds, but it should slow down a joy rider. A sneaky theft prevention idea: Bypass the switch with a 15 amp fuse. All would appear normal until the thief tried the starter. Then, nothing.

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