DIY: door lock with aftermarket alarm
 

I have a compustar remote start/alarm that outputs (-250mA) for locking and unlocking.

The RX-8 uses a single wire locking scheme, where it locks when it gets a ground signal thru a 1000ohm resistor , and unlocks when it gets a chassis ground.

instead of buying the DEI 451m module and making that work i decided to use a standard relay i had laying around:

For UNLOCKING you need a relay
Connect:

87 - chassis ground
87a - unused -
86 - fused 12V
85 - unlock signal from alarm
30 - Lt Green door lock wire of the car

at rest (no unlock signal) the relay will connect 30 to 87a, in this case its unused and does nothing.

when it gets an unlock signal thru 85, it connects 30 to 87 instead, grounding the circuit in this case. this ground is passed thru the relay thru 30 and into the ltGreen wire... where it will trigger the unlock.

For LOCKING:

simply add a 25cent diode to the LOCK output of the alarm, then add a 1000 ohm (1Kohm) resistor, and connect to the light green wire. when you press lock the signal passes one way thru the diode then thru the resistor , and this added resistance triggers the lock.

thats the theory behind the lock, but even if you leave out the resistor it still works, at least it did for me. maybe the bad soldering added some resistance?

no relay is needed for the locking.


Hope this helps someone out in the future.