Struggling to fit an after market alarm.

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Topic author
davielad
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Joined: 02/10/15 17:40

Struggling to fit an after market alarm.

Post by davielad » 02/10/15 17:58

Hi Folk,
I've just successfully removed THREE old redundant car alarm systems from my MK1 and the time has come to fit a new one.

The new one requires a 12v input from the door open switch and a 12v input to confirm the handbrake is on. Does anyone know where I would get these signal wires from?

I took the dash apart but could only meter 12v on the handbrake lamp when it was off? (I might need to install a relay?)
Also the "door" light seemed the best option for the door signal but metering that out makes no sense to me as it seems to get a switched neutral?

Is there a nice easy spot to get these two signals from? :confused1:



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jimi
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Re: Struggling to fit an after market alarm.

Post by jimi » 02/10/15 19:08

You won't be able to get a +12ve signal from the handbrake or the door switches, Mr T doesn't wire things up like that, his switches are nearly always on the earth leg not the supply leg.
i.e +12v ->lamp -> switch -> earth. Also the handbrake switch is only active when the ignition is on i.e. no voltage going to it when the ignition is off.
Most modern alarms I've seen are configurable to allow the use of inputs or outputs for sensing. If yours only works with inputs your going to have to be creative with relays.
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Re: Struggling to fit an after market alarm.

Post by davielad » 04/10/15 12:46

Thanks Jimi.
It seems your right! This is going to be a mission i think but hope its worth it in the end. I've got the wiring diagrams printed out now so i will figure out some way of getting these inputs if it kills me.
The new system has "auto start" which will be amazing on a cold winters morning to get things warmed up at 5am before i start my shift work. Thats the reason for all the safety inputs it needs.

I'll hopefully repost an update once I've got it sorted.

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Re: Struggling to fit an after market alarm.

Post by jimi » 04/10/15 19:03

davielad wrote: It seems your right!

I hope so :)
Jimi's Profile wrote: Occupation: Chief Electrician
Interests: Cars, computers, electronics, .......
;)
The new system has "auto start" which will be amazing on a cold winters morning to get things warmed up at 5am before i start my shift work.
Bear in mind that it's illegal to leave a vehicle on a public road unattended with the engine running ;)
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davielad
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Re: Struggling to fit an after market alarm.

Post by davielad » 04/10/15 19:12

My wife got fined for that once! Crazy. I will be sure its on my driveway. ;-) Thanks


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davielad
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Re: Struggling to fit an after market alarm.

Post by davielad » 04/10/15 20:56

Might this work?
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davielad
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Re: Struggling to fit an after market alarm.

Post by davielad » 04/10/15 20:56

Might this work?
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Re: Struggling to fit an after market alarm.

Post by jimi » 05/10/15 5:56

Yes that will work, I've used that method before.
You can also do the same with the door switches
Put the diode just after the light (possibly in the light ?) before the circuit splits to either door, that way either door switch will operate the relay.
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davielad
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Struggling to fit an after market alarm.

Post by davielad » 06/10/15 21:03

Thanks again Jimi.


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