Wiring Alarm/Central Locking w/Isolation Switch

Hi All,

My defender runs a T-Max split charge set-up and I run them through n isolation switch to kill electrics when away from the vehicle.

I want to install a fairly cheap and simple Alarm (Movement based) and central locking set-up (HAWK System), but obviously, wiring up to either battery will kill the system when I take the isolation out.

Could I run the Alarm/CL earth straight to the chassis to bypass the isolation? What worries me is then that creates a short which may end up with way to much current being chucked down the alarms lines as the whole system may try to earth through it ...

What are my options here?

Or have I got my theory upside down inside out here?

Thanks all ...

I thought most isolation switches only switched the positive supply, does yours do both + and -ve?. If it only switches the positive then connect the earth to a suitable chassis point and connect the positive to the battery side of the isolation switch (via fuse of course). That will ensure the alarm/CL will have a supply even with the isolator off. If however it switches both sides then you are a bit buggered unless you either it rewire to a single side or run the alarm/CL earth wire to the battery negative terminal.

Earth is usually common to everything and not isolated

If your worried about the alarm earth being overloaded fuse that too

bridge the isolation switch with a 1 amp fuse. this will be enough to keep the alarm etc running, plus radio codes etc when the switch is in the off position.

However, when anyone tries to start the vehicle, the current is way more than the fuse can handle and then the fuse will blow and the vehicle won't start until the switch is turned back on again.

preferably fit an alarm with a self contained battery so it will continue to sound even when the main supply is removed. As for the central locking, in the event of the fuse blowing by someone trying to start the vehicle, you would have to use the key to gain entry.

If you think there is the possibility of leaving your lights on when you turn the isolator off, which would cause the 1 amp fuse to blow, you may wish to consider fitting a larger fuse which could handle the total load of the lights which would still be less than that needed to start the vehicle, or a lights on warning buzzer.

good luck

Optimus Prime said:

bridge the isolation switch with a 1 amp fuse. this will be enough to keep the alarm etc running, plus radio codes etc when the switch is in the off position.

However, when anyone tries to start the vehicle, the current is way more than the fuse can handle and then the fuse will blow and the vehicle won't start until the switch is turned back on again.

preferably fit an alarm with a self contained battery so it will continue to sound even when the main supply is removed. As for the central locking, in the event of the fuse blowing by someone trying to start the vehicle, you would have to use the key to gain entry.

good luck

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That's a plan, however if you were to park up and forgot you left your lights on then opened the isolator the lights current would blow the fuse, meaning alarm/CL inoperative until you change the fuse.

i used a 30A fuse in my bypass, its man enough to cope with the lights (on the 300, it goes down to sidelights anyway with the engine off) but will still blow if you try and crank the engine.

Kwakerman said:

That's a plan, however if you were to park up and forgot you left your lights on then opened the isolator the lights current would blow the fuse, meaning alarm/CL inoperative until you change the fuse.

Click to expand...

until you catch the main beam flash with your knee when your getting in lol

Kwakerman said:

That's a plan, however if you were to park up and forgot you left your lights on then opened the isolator the lights current would blow the fuse, meaning alarm/CL inoperative until you change the fuse.

Click to expand...

think you need to re-read my post...

Are you sure you didn't sneakily edit that in ??? - either that or I was still half asleep when I read it!

Kwakerman said:

Are you sure you didn't sneakily edit that in ??? - either that or I was still half asleep when I read it!

Click to expand...

Now you need to read my signature quote by minty...