97 UK TJ - wiring central locking into remote immobiliser fob? - Jeep Wrangler Forum

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Old 09-04-2011, 01:32 PM
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97 UK TJ - wiring central locking into remote immobiliser fob?

Hi Guys,

I have a 1997 TJ Wrangler Auto (4 litre) which has a factory UK immobiliser fitted which has an arm/disarm key fob (the black Chrysler fob with a lock and unlock button). It doesn't have central locking. I purchased an aftermarket central locking kit which has an input to activate/deactivate the central locking when connected to an "alarm/immobiliser system".

I have now fitted the central locking system and it is working fine with the key in the door, so I can lock/unlock the vehicle and the 2 doors and tailgate lock/unlock together.

What I want is to wire the activate/deactivate wiring into my immobiliser so that when I click the fob it locks/unlocks the car as well as deactivating the immobiliser.

The kit requires either a momentary short between the "lock" and "unlock" wires on the kit, or a short between "lock" and ground to lock, and a short between "unlock" and ground to unlock the car.

The immobiliser is mounted behind a metal plate behing the speedo gauges. It has a bunch of outputs, some of which are not used. My plan is to wire the central locking into the immobiliser so that it will lock/unlock when I hit the fob. I've been over the pins on the immobiliser with a multi-meter, and I've found a constant 12v between 2 pins only when the immobiliser is active, there is 0v when the immobiliser is deactivated. What I thought is that if I put a 5 port relay on those pins, it will close when the immobiliser is on and open when it is off, I can then wire lock and unlock appropriately (to ground) via the 2 switch positions, so that it will lock and unlock at the right times.

I've mocked this up in the house with a spare car battery and it all works. Problem is that in the car, I can't get the relay to switch when the voltage it active. Measuring it on the multimeter it is 10.9 volts. I connect the appropriate relay pins to the immobiliser when I switch it on and off, but the relay never trips. I am not sure if it isn't enough current, or the 10.9 volts is too low to trip the relay. I have also found a 6.2v pin, so I was thinking I could maybe try a 6v relay, but those are harder to find and I am worried about putting it in the car with a 12v system.

I have tried 3 12v relays, a 30A 4-way relay, a 40A 5 way relay and a 6A 5 way relay. None trip on this 10.9v. They all trip when I connect them directly to my battery (briefly) or to the car battery accessory wire.

Any help with this problem would be massively appreciated.

Alternative is to remove the immobiliser completely and buy a separate fob and wire that directly into the central locking. Issues with that is that it will be more expensive, take away my immobiliser which is a security feature and will remove my nice factory Chrysler fob and replace it with a nasty aftermarket one.

It's got to be possible to get this working, I feel like I'm so close. Thanks in advance for any help guys.

1997 Wrangler TJ 4.0L Sahara Automatic, Black
1989 BMW 635 CSi Highline Motorsport Auto, Misano Red
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