Door Lock Circuit Modifications and Maintenance

Created: 9/21/1998

Last updated: 6/3/03

Author/source: Swingle+others

ADDED RESOURCE 10/08/02 - Submitted by :  Elvis Nocita, DML'er of Germany.  elvisnocita(AT)

This is a great contribution to the ongoing study of the lock control module, including instructions and photos of how to upgrade the module to reduce its standby current consumption for increased battery life. Assumes that you are slightly competent with electronics. Large (400k) downloadable PDF file. 

Download HERE (right-click and save recommended)

ADDED RESOURCE 6/3/03 - Submitted by :  Dave Stragand

How to rewind your own solenoids and save big money


Modifications to the Door lock Solenoid Circuitry to make it much more Robust

I worked up something on my locks to fix the problem with the stock logic box. You might have a good time with this and save a bunch of money. Everything I mention here adds up to about $35.

I have a set of schematics and info drawn up here:

Lock Circuit Board Detail

Lock Circuit Diagram - Corrected 10/01

Lock Modification

1. Test the lock solenoids by unplugging the lock module and hot-wiring them to battery at the connector plug. Each solenoid has two coils, one for lock and one for unlock. With the large connector unhooked, you can hot-wire each coil in turn to the breaker and see if the solenoids make noise in the doors. You probably have one or more burned out. These can be replaced for $110 apiece, or you can take them apart and rewind them for about $10 worth of wire. These must work before you do anything else, or you'll just fry everything. Each solenoid coil takes about 70 feet of #20 enameled motor wire. Get from an electric motor repair place. Also make sure that the breaker is good.

2. Open up the existing lock module and make sure the relays aren't stuck. If they are you can usually just unstick them. The module is not sealed, just slide the tie-wrap off the end and it opens.

3. Go to Trak and buy two 81-89 Chrysler Starter Relays, Gen Automotive #32870, about $12 ea. Also get some assorted colors of #12 stranded wire and a bunch of crimp connectors. You'll also need two 1N1007 diodes from Radio Shack for about 59 cents. These relays get wired in series with the existing lock module. This means the lock module is now only controlling the relays, and the starter relays are feeding the solenoids. The solenoids are much less drain than a starter so they should last forever. The can be mounted next to the existing lock module. You have to open them up, clip out the diode inside and solder the 1N1007 diode across the appropriate connections.

I have this all done on my car and it works great. You need to make three solder connections, everything else is crimp-on terminals and is easily reversible.

update 10/1/01

Here's a nice theory of operation submitted by Martin Gutkowski. This will help if you are electronically inclined. He also submitted the corrected drawing. One of these days I'll fix the original, but since I converted from a Mac to a PC I've lost the artwork. ---dave

Lock Circuit Diagram - Corrected 10/01

Hi Dave

As I said before, my memory of electronics is sketchy at best. My friend Nathan actually went to work for Sony after university and consequently was
the right person to reverse-engineer your diagram. Below is his comments on the circuit and attached is the corrected diagram.

Feel free to add/use his comments on the DMCnews site. Disclaimer applies - (You'll read it at the bottom :-)

His name's Nathan Bentall


Martin Gutkowski
DOC UK Webmaster

-----Original Message-----

From: Nathan

OK, don't kill me if this is wrong - I cannot find any info on BRF34 which doesn't help.

Half-assed explanation:
Switch in 'lock' position. point A is at 0.6 v, Q1 is off & C1 discharged.
Meanwhile, point B is _not_ grounded through D5, so is pulled up through R12. This has switched on Q11 to charge up C11 through R11, so point C is now at 11 ish volts. Now I change to the 'unlock' position. I have now grounded (via a diode) point B, but point C is still 10 ish volts due to C11 being still charged up, so it discharges through the relay coil and R11 causing the relay to be on. After a short time, this charge runs out, and the relay returns to it's normal position. The lower and upper circuits have now exchanged states and the upper circuit is ready to lock again (after a little time for C1 to recharge). Due to the relay being switched by the capacitor, you can see why some knob at Lucas thought protection diodes were unnecessary since under normal operation, there can be NO BACK EMF from the relay... almost clever... unless... you waggle your key in the lock or your door switches are dodgy/dirty, in which case, you might fry your diode/cap pair as you could loose your ground before the cap has discharged  which may (only may, mind you, depending largely on the inductance in the relay, I think) cause point B (A) to shoot above the rail. A pair of 13 ish volt Transzorbs would do the trick here (unusual for me to recommend traszorbs, I know! - Transzorb is a trademark I think. basically, it is a fast avalanche diode that can dissipate large amounts of energy for a very short period of time and recover. Used to stop spiky voltages damaging things). Connect them between point A & gnd and point B and gnd. Alternatively, a pair of fast, small ish rectifier diodes connected between points A and 12v and point B and 12v (pointing towards the 12v) would be equally good.

This fault in the circuit means quite possibly - under this circumstance, the relays could feasibly switch quickly, which could knacker them (assuming the transistors survived). This could cause them to stick for an entirely different reason than simply being underrated for the solenoids. A better circuit would isolate the switches with some kind of buffer with Hysteresis.

DISCLAIMER: This information, if not entirely wrong, is probably mostly so. If you have read this, you must not use your DeLorean as a life preserver, artificial lung, defibrillator, as, or in conjunction with, any other kind of life support system - if your DeLorean IS your life, then you are sad - it's just a car and will never get you girls like knowing about computers will.


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