Alarm swap: external to internal kill relay

I have a 1995 bmw m3 that has an old alpine alarm in it (sec-8027a). That alarm died so I purchased a viper 3606v. My old alpine has an external starter kill relay, the new viper has an internal starter kill relay. All the wires are already run so I'd rather not have to go digging into the drivers side to change the starter kill wiring over. What i'd like to do is replicate the single +12v output of the alpine so i dont have to rewire/remove the existing relay.

The viper alarm has 3 wires for starter kill, common(key side), starter NO, Starter NC. Can anyone give me a reason the following wont work. I'd like to dump 12v into the common/key side of the internal relay and then connect the Normally open wire to the existing starter kill relay. To my mind this should put 12 v out to the existing starter kill relay when the alarm is armed and mean I dont have to go dig out the existing relay from the dash.

B

The correct way to accomplish what you want to do is to connect the Viper's Ground when Armed output (H1/12) to the relay's coil. The other side of the Relay's coil should be wired to ignition (+) signal (also goes to Viper H3/5). There also may be a diode across the coil, with the band toward the Ignition (+) wire--this is recommended but sometimes omitted. The ignition (Key side) and Ignition (Motor side) should still be wired to the external relay. No need to use the Viper Starter kill wires at all.   

For a normal 12V relay, this would be:

Relay 86: Ignition (+) --From Viper and Car
Relay 85: Ground When Armed--From Viper
Relay 30: Key side of start wire--from Car
Relay 87A: Motor Side of Start wire--From Car
Relay 87: No connection


Note that Relay 87a and 30 are normally closed contacts and may be interchanged.
Note that a 1n400x (x may be 1-7, i.e., 1n4002) with band toward Ignition (+) is recommended across Relay 86 and Relay 85.

If you want to use the Viper starter kill in series with this relay, you would cut the starter wire and connect viper starter kill key side wire to the key side of the start wire, and Viper starter kill Starter NC wire to the motor side of the start wire.
The Viper has an option setting for the immobilizer (Starter kill) that is default for NC Starter kill. If you change that option to NO starter kill, you would need to connect the Viper's NO starter kill wire to the motor side instead of the Viper's NC starter kill wire, your choice.    

Hope this helps.



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Lectric Guy

Hrm, thats actually clever. That way the relay coil isnt energized the entire time the alarm is armed. It should only energize and cut the starter wire when the alarm is armed and someone actively tries to start the car.

B

Correct. If the relay is powered when the alarm is armed, you will eventually run into a dead battery issue...

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Lectric Guy

Cool, Since the starter kill is already wired up and expects a single +voltage signal to cut the starter I will just tap power from the ignition wire, which already exists at the alarm unit, and dump that through the starter kill relay. Then when armed and someone goes to start the car the ignition wire will go live and power will run through the starter kill relay and trigger the existing starter kill relay. However if unarmed starting the car should work fine as the +v from the ignition will never make it through the starter kill relay to cut the starter.

Basically, I just dont want to have to go find the existing starter kill relay.....

Brian

OK, remove 87a and 80 wires from relay and join to the green/white and green/black wires from the 3606. Ignore the green.
Far more simple and you win a relay.
PS if you go with the idea above, a 1N4004 diode is mandatory else you'll fry the GWA circuits on the 3606.

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Amateurs assume, don't test and have problems; pros test first. I am not a free install service.
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