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TESTING: Door Locks
There are three basic types:
“Type A” Door Lock Test (Most GMs and some Chryslers)
Probe both of your door lock wires going to the door lock switch usually located in the driver’s kick
panel. Attach the clip end of your test light to a good chassis ground. Using the vehicle’s door lock
controls, activate the lock then the unlock, testing both wires one at a time. If one of these wires
tests (+) positive when lock is pressed and the other tests (+) positive when they are unlocked, your
vehicle has a “Type A” door locking system. Make sure to mark which wire is lock and unlock. Proceed
to Connecting Door Locks, Connecting Door Locks. NOTE: “Type A” and “Type C” locks will test the same,
until you test for ground. Make sure you run both tests before making your connections.
“Type B” Door Lock Test (Most Imports, some newer Fords)
Probe both of your door lock wires going to the door lock switch usually located in the driver’s kick
panel. Attach the clip end of your test light to +12V. Using the vehicle’s door lock controls, activate
the lock then the unlock testing both wires one at a time. If the test light illuminates when you probe
the lock and the unlock wires your vehicle has a “Type B” door locking system. Make sure to mark which
wire is lock and unlock. Proceed to Connecting Door Locks.
“Type C” Door Lock Test (Most Fords, some Chryslers, GM Trucks)
(Optional part #778 required)
Using your test light probe both the lock and the unlock wires usually located in the driver’s kick
panel. Attach the clip end of your test light to ground probing both wires one at a time while
CONNECTING “TYPE B LOCKS”
• If your vehicle has a “Type B” door locking system,
connect the GREEN WITH BLACK STRIPE wire from the
18-pin harness to the door lock wire. Connect the
BROWN WITH BLACK STRIPE wire to the unlock wire.
See diagram below.
“Type B” - Negative type door locks used on most
imported vehicles and some newer Fords.
BROWN/BLACK
LOCK
UNLOCK
GREEN/BLACK
“Type A” - Positive type door locks used on most
GM, some Chrysler vehicles.
GREEN/BLACK
LOCK
UNLOCK
BROWN/BLACK
CONNECTING DOOR LOCKS
(Optional)
CONNECTING “TYPE A LOCKS”
•If your vehicle has a “Type A” door locking system,
connect the BROWN WITH BLACK STRIPE wire from the
12-pin harness to the door lock wire. Connect the
GREEN WITH BLACK STRIPE wire to the unlock wire.
See diagram below.
CONNECTING “TYPE C LOCKS”
•If your vehicle has a “Type C” door locking
system, you will need to purchase optional part
#778. Once you have purchased the relays, follow
the diagram on page 18 for “Type C” door locks.
TYPE C - (Optional Part #778 required)
Reverse polarity door locks. Used on most GM
trucks, Ford and Chrysler vehicles.
87a
BLACK
RED
BLUE
BLUE
YELLOW
WHITE
BLACK
RED
locking and unlocking the doors with the driver’s side switch (usually the master switch). The test
light should illuminate in both switch positions. Now attach the clip end of your test light to +12V
constant, probe both wires one at a time again. The light should then illuminate again only in reverse
order. This tells you that you have a “Type C” reversing polarity system. Make sure to mark which wire
is lock and unlock. Proceed to Connecting Door Locks.
Testing Switch Wire and Motor Wires
Before connecting, you must now determine which wire is the switch wire and which is the motor
wire. Cut both the lock and unlock wires in half. Start with both of the lock wires by placing
the clip end of your test light to ground, hold the door lock switch in the lock position, make
sure you are using the master switch (usually on the driver’s door) and probe both lock wires
looking for voltage. The wire that illuminates the test light, mark as the switch wire, the wire
that shows no voltage, mark as the motor wire. Repeat the procedure for the unlock wire. When
connecting the lock and unlock wires to the #778 relay harness, make sure you connect the switch
wire to the RED wire or pin #87A and the motor wire to the BLUE wire or pin #30. Be sure to connect
the lock wires to the lock relay, and the unlock wires to the unlock relay, you may need to mark
these relays before you start.