OE remote interfacing

Printed From: the12volt.com
Forum Name: Car Security and Convenience
Forum Discription: Car Alarms, Keyless Entries, Remote Starters, Immobilizer Bypasses, Sensors, Door Locks, Window Modules, Heated Mirrors, Heated Seats, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=29836
Printed Date: July 22, 2025 at 9:54 AM

Topic: OE remote interfacing

Posted By: naughtydog
Subject: OE remote interfacing
Date Posted: April 06, 2004 at 4:56 PM

I use quite a few of the Hornet 700T in the Uk for certain vehicles. For those that dont use them they are an alarm that works from the vehicles OE transmitter.

Today I did a vehicle (Citroen Dispatch - French POS) and hit a problem.

On this vehicle if you use the door motor wires to turn the alarm on/off you can just unlock the key in the door and cancel the alarm - no good!!

At the vehicle control unit I found a spare pin which gave a negative output on unlocking via the OE remote but not with the key...just the job - or so I thought.

Because this wire only pulsed a neg on unlock and rested open or floating, the Hornet would not see this wire as a disarm command. I added a relay to the wire so the hornet would see a full positive when unlocking via the relay. The output from the vehicle would not pull in a normal 12v relay - aagh!!

What else could I have done??. I think a little transistor to switch the low output could have been used but I am not that into the electronics thing enough to come up with a solution.

I tried to disable the door lock wire from the key barrell, but as the cental locking is single wire control, once the wire was cut, the doors locked...in the end I fitted another alarm with a seperate handset.

Any ideas anybody

Naughtydog

Replies:

Posted By: Big Dog
Date Posted: April 07, 2004 at 9:56 AM

Hey Naughtydog,
From one dog to another . . . reconnect the Hornet's Blue and Green wires to the motor wire then locate the Disarm Defeat (Red) wire from the Hornet and connect to the keyswitch wire. Now try the system again. If the Hornet sees a signal on the Disarm Defeat at the same time as the Blue unlock wire then it will refuse to disarm. This is why it's called Disarm Defeat. posted_image

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Prepare your future. It wasn't the lack of stones that killed the stone age.

Posted By: naughtydog
Date Posted: April 07, 2004 at 3:25 PM

aagh...now why did'nt I think of that. Next time I do one I will try that.
Doeas the Hornet only disarm defeat with a negative. In fact, I remember trying it and does give a negative on unlock so that should work

Thanks

Naughty

Posted By: Big Dog
Date Posted: April 08, 2004 at 7:56 AM

The disarm defeat wire is bi-polar depending upon the polaririty learned for the door lock wires. If the Hornet learned the unlock as being positive then the disarm will look for positive and vice-versa.
When the prouct is well engineered the solutions are usually simple. posted_image

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Prepare your future. It wasn't the lack of stones that killed the stone age.

Posted By: naughtydog
Date Posted: April 12, 2004 at 3:31 PM

Thanks Big Dog,

To summarise, if my motor unlock is positive, then my disarm defeat wire will be looking for a positive also??...therefore, I will need to add a relay to change over the negative unlock command from the door switch unlock wire ( not motor unlock ) and connect to the diarm defeat wire.

Thsi should then work OK - correct?

Naughtydog