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1989 Porsche 944 Turbo Auto Unlock

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=124369
Printed Date: May 13, 2025 at 6:49 PM


Topic: 1989 Porsche 944 Turbo Auto Unlock

Posted By: sdpatton
Subject: 1989 Porsche 944 Turbo Auto Unlock
Date Posted: November 09, 2010 at 11:50 PM

I put a Scytek G20 in my 1989 Porsche 944 turbo, primarily for remote keyless entry; it has auto lock/unlock but it is based on the ignition switch, on/off = lock/unlock, and that doesn't work for me; it's not uncommon for me to start it, get out and close the door to have a look under the hood or some such task

what I want to do is one based on the parking brake and powered by the ignition (the parking brake has a little switch, much like a door contact, when it is set, the circuit is closed and provides a grounded connection, when it is released it opens the circuit):

  • if the car is not started, then set/release the parking brake will do nothing to either the lock or unlock circuit
  • if the car is started, changing from set to released will pulse a ground to the lock circuit
  • if the car is started, changing from released to set will pulse a ground on the unlock circuit

I haven't had to deal much with relays, diodes or even ohms-law since college (late 80's) so it's been a while; looking at the standard "Add Auto Lock/Unlock w/o Alarm" they are also based on ignition on/off = lock/unlock, so as they are, they do not fit my needs

for the unlock I can see where I could repleace the 'pink' circuit section (ignition 12v(+) and the diode)  with the connection to the parking brake switch; I breadboarded it up (haven't done that in 20 years either), and it appears to work, in theory, grounding the bottom of the cap and resistor the relay pulses; the only problem I see is that it takes several seconds for the cap to discharge before I can trigger the circuit again

I haven't given much thought to the auto-lock, as I'm much more interested in the auto-unlock; the central locking system won't unlock, via the button, after ignition is off, so I have to put the key back in to "Run" then unlock, but 99.99% of the time, I set the parking brake before turning the car off, so this is very useful to me

any thoughts on the best ways to accomplish this would be appreciated...thanks

P.S. I think it would be very helpful to note in the circuit diagram for "Add Auto Unlock w/o Alarm" that it is asssumed when the ignition is turned off, it provides ground to close the circuit; the notation of "ignition 12v(+)" is quite confusing, IMHO


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