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Type A: Three-wire (+) pulse controlling factory lock relays
The system can control Type A door locks directly, with no additional parts. The switch will have three
wires on it; one will test (+)12 volt constantly. The others will alternately pulse (+)12 volt 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 (+)12 volt alternately on lock and
unlock, make sure that it is not a Type C direct-wire system.
Here is a test: Cut the wire that pulses (+)12V on lock, and then operate the switch. If the locks stop work-
ing, then you have the correct wire.
Many GM vehicles use Type A locks. However, some GM vehicles are Type C. This system usually appears
in older GM vehicles (1980-1995). The full-size pickups (1989-up), many of the Blazers, the Corvette,
1995 Cavalier/Sunfire 1993, and the newer Camaro/Firebird, all use Type C door locks, and cannot be
controlled without relays.
Almost all newer Fords are Type B. Ford builds no Type A systems. Chrysler now uses multiplex door lock
systems (Type G or H) that require relays and resistors to properly interface the circuit.
Important: Remember that these wires function in the reverse for Type
A and Type B.
(-)
(-)
(+) 12V CONSTANT
(+) 12V CONSTANT
(+) 12V CONSTANT
GREEN
BLUE
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