26 © 2000 Directed Electronics, Inc. Vista, CA
The system can control Type A door locks directly, with no additional parts. The switch will have three wires on
it, and one will test (+)12V constantly. The others will alternately pulse (+)12V when the switch is pressed to
the lock or unlock position.
If you cannot get to the switch, and you find a set of wires that pulse (+)12V alternately on lock and unlock,
you must take care to ensure that it is not a Type C direct-wire system.
Here is a test: Cut the wire which pulses (+)12V on lock, and then operate the switch to unlock.
■ If all doors unlock, the vehicle uses type A system.
■ If you lose all door lock operation in both directions, you are operating the master switch in a Type C system.
■ If you lose all door lock operation of one or more, but not all motors stop operating, and other doors still
work, you have cut a wire leading directly to one or more motors. You must instead find the actual wires
leading to the switch.
Many domestically-made GM vehicles use Type A locks. However, many more GM vehicles are Type C than in pre-
vious years. The full-size pickups (1989-up), many of the S10 Blazers, the Corvette, '95 Cavalier/Sunfire 1993
and newer, Camaro/Firebird all use Type C door locks, and cannot be controlled without a 451M! Almost all
domestically-built Fords are Type C. Ford builds almost no Type A systems. Chrysler builds both Type A and Type
C, so use care.
IMPORTANT! Remember that these wires' functions reverse between Type A and Type B!
type A: (+) 12V pulses from the switch to the factory relays
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