3157 3157 SR CK 3156 7443 CK 7440 Wiring Diagrams

This can be seen in the wiring diagram below.  

Conventionally Wired 3157 and 3156 Led Bulbs

Conventionally wired 3157 / 3156 Led bulb	3157 SRCK SACK Led Bulb

3157

The 3157 is a dual contact (d.c.) bulb (Conventional 3157 Led Bulb shown left).  The dual contacts are connected to 2 separate circuits inside the bulb.  One circuit is for bright  or high beam (braking/turn signals) and one for dim or low beam (running/parking lights).   

The 3157 has four separate wire contacts protruding from the bottom.  If you examine the bulb closely, you can see that two of the wire contacts connect to the same point inside the bulb.  These two contacts are the common negative (-) grounds.

Note: Use Special 3157-SRCK (Red) or SACK (Amber) bulbs to replace the center tail lamp bulbs on:

•  88-99 (Old Body Style) Chevy and GMC full size trucks & SUVs.

•  95-01 Cavalier and Sunfire tail lamp bulbs

• 92-98 Grand Am tail lamp bulbs

• 88-99 (Old Body Style) Chevy and GMC full size trucks & SUVs.

•  95-01 Cavalier and Sunfire tail lamp bulbs

• 92-98 Grand Am tail lamp bulbs

These special 3157-SRCK (Red) or SACK (Amber) bulbs are available :

CLICK HERE TO >> ORDER SPECIALLY WIRED SRCK & SACK BULBS

We are also finding other vehicles that are sometimes wired this way.  As you can see from the diagrams, a regular 3157 led cannot be easily altered to make it into an SRCK:

Conventionally wired 3157 / 3156 Led bulb	3157 SRCK SACK Led Bulb

3157 SRCK/SACK Led Bulb

Symptoms:

If you use a conventionally wired 3157 led bulb in a socket that is wired for the SRCK/SACK led bulb, the bulb will pop the fuse when the lights are switched on.  If you remove the bulb, rotate it 180 degrees and reinsert,  it will not light at all.

If you use a 3157 "CK" bulb in a socket that is wired for a conventionally wired 3157 led bulb, it will work properly in bright mode, but it will not light in dim mode.  If you remove, rotate the bulb 180 degrees, and reinsert, it will not light at all.

Testing:

You can test how your sockets are wired using a multi-meter.  Just set the meter to ohms an find the common ground contacts in the socket.  These contacts will be common to any metal ground point on the vehicle and will register a zero or very low resistance reading on the ohmmeter with any common ground point.

Fixes:

If you find that you have 3157 'CK" sockets and 3157 conventionally wired led bulbs, there are two solutions:

1.  Swap the conventionally wired 3157 led bulbs for the 3157 "CK" led bulbs.

2.  You can swap the wires to the socket to match the diagrams above.

3156

The 3156 is a single contact (s.c.) bulb.  The 3157 led bulb can be used universally in either 3157 or 3156 applications.  We usually ship 3157 bulbs, unless the 3156 is specified in the order, to provide the greatest flexibility of application for the user.

The 3156 has two separate wire contacts protruding from the bottom.  One of these two contacts is the common negative (-) ground. The remaining contact is the positive (+) side of the circuit.  The 3157 extra contacts don’t connect to anything in the 3156 socket and the bulb will light high beam only in the 3156 socket.

  7443 to 7440 conversion

7443

Note: The 7443 led bulb will function in either 7443 or 7440 sockets.  In the 7440 socket, the 7443 will have extra contacts that are not connected to anything.  The 7440 will not function in the dual bright dim mode in the 7443 socket.

This can be seen in the wiring diagram below.

The 7443 is a dual contact (d.c.) bulb (Shown left).  The dual contacts are connected to 2 separate circuits inside the bulb.  One for bright  or high beam (braking/turn signals) and one for dim or low beam (running/parking lights).   

The 7443 has four separate wire contacts protruding from the bottom.  If you examine the bulb closely, you can see that two of the wire contacts connect to the same point inside the bulb.  These two contacts are the common negative (-) grounds.

7440

The 7440 is a single contact (s.c.) bulb.  The 7443 led bulb can be used universally in either 7443 or 7440 applications.  We usually ship 7443 bulbs, unless the 7440 bulb is specified in the order, to provide the greatest flexibility of application for the user.

In a very few vehicles, the low and high + Positive leads on the 7443 will need to be bent to the opposite sides so that the bulb will light on the brighter high beam circuit in the 7440 application.   If not sure which 2 leads are the positive leads, just  bend all leads around to the opposite sides.  This will ensure that the high beam circuit connects to the high beam contact on the bulb.  Use care when bending the leads and only bend one time to avoid breaking them off. The leads should only be bent one time.

The 7440 has two separate wire contacts protruding from the bottom.  One of these two contacts is the common negative (-) ground. The remaining contact is the positive (+) side of the circuit.  The 7443 extra contacts don’t connect to anything in the 7440 socket and the bulb will light high beam only.

To find out if these bulbs will fit your vehicle..........

Click Here>>  http://www.sylvania.com

Then go to:  Automotive Replacement Guide - find the right light source for your vehicle