Wiring a bypass for the alarm

[ldtopham]

I am just getting the parts together to fit a battery isolator. I am using a Durite removable cut key style isolator but would like to retain the supply to the alarm and radio using a fused bypass. I use this type of isolator on another vehicle and think it is a good bit of kit.

The plan is to be able to isolate all the electrical circuits apart from the radio (to save re-entering code) and alarm system. My questions are:

1. Has anyone checked the current draw when the alarm and siren sound?

2. If it is possible to fit a bypass supply to the alarm system where can I pick up the supply wire for the alarm system? (I appreciate this is an open forum so please PM this one)

3. Does the standard Land Rover alarm system have a battery back up for the siren if supply voltage is lost?

Thanks in advance.

[dave88sw]

I cant say how much current is drawn by an alarm but the simplest way to power a radio and alarm with a standard isolator is simply to bridge the contacts of the isolator with a piece of wire and inline fuse of suitable ampage. You'll find most things work until the fuse rating is exceeded and if they try to start the vehicle the fuse blows and nothing works.

However when i did mine i just ran a wire direct from battery to radio memory wire, i don't have an alarm.

Hope that helps

Dave

[ldtopham]

I cant say how much current is drawn by an alarm but the simplest way to power a radio and alarm with a standard isolator is simply to bridge the contacts of the isolator with a piece of wire and inline fuse of suitable ampage. You'll find most things work until the fuse rating is exceeded and if they try to start the vehicle the fuse blows and nothing works.

However when i did mine i just ran a wire direct from battery to radio memory wire, i don't have an alarm.

Hope that helps

Dave

Thanks Dave, I am going to wire it as you suggest. Just trying to find a location that is secure for the isolator.

Regards,

Lee

[RichardAllen]

Thanks Dave, I am going to wire it as you suggest. Just trying to find a location that is secure for the isolator.

Regards,

Lee

Lee,

On my 90, the power to the alarm goes through Fuse 20 (bottom right) in the passenger compartment fusebox, (I got this from the wiring diagrams in the RAVE electronic manual set available as a download) so you could start from there or the equivalent on your vehicle.

Regards

Richard

[ldtopham]

I've borrwed a clamp meter from work and will measure the current draw with the alarm armed and with it sounding with everything else switchwed off. The interior light and radio memory feed are the only other accessories I can think of that will draw current through my bypass. If I inadvertantly tried to start the vehicle without turning the main supply on I guess removing the cover to the repalce the 20amp fuse would soon prove annoying. With this in mind I am going to fit an inline fuse to a location that is easy for me to access, not so obvious for others and hopefully less than the 20amp rating of the one you mention....I'll know tonight when I have metered the battery cable.

Thanks.

[ldtopham]

Quick update if it's any use to anyone else:

All accessories turned off = 0.1amp current draw (radio memory/ clock)

Arm the alarm = 5.3 Amps

Alarm sounds horn/ siren and indicators flashing 14.2 Amps

Ign on 42Amps reducing to 30 Amps over glow plug heater time. After heater relay times out 2.5 Amps with Ign on.

Crank/Ign =394 Amps

Interior light draws 1 Amp

I measured on the battery positive cable beneath the passenger seat.

So for the battery isolator bypass fuse I reckon a 20Amp fuse will do just fine. The radio memory, clock, alarm (activated) will all sound without tripping the fuse and as soon as another accessory is turned on or Ign is turned on the fuse will break. I know this isn't the best line of defence and could easily be worked around but every little helps