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3157 Switchback Switch Back Led Turn Signal Bulb Installation Wiring Troubleshooting Tips

Very Important Note:  Led light bulbs do not have brains. computers or complex logic chips built in.  Automobile circuits on the other hand often do have brains,  computers and/or complex logic chips built in.

 

While the led bulbs are very simple, automobile circuits on the other hand are very complex and vary even within the same models.  When you plug an led bulb into a circuit, you are not testing the bulb itself, you are testing  a system which includes circuitry, battery, + the led bulbs.   If the led bulb is not functioning as anticipated, the problem may lie in any part of the system.  The bulb only serves as an indicator for what the system is doing. 

 

Led bulbs and glass bulbs may make the circuit/system operate differently, so never use a glass bulb to predict how the circuit will operate with an led bulb installed.

Here is all you really need to know:

 

The switchback leds bulbs are very simple.  They light white when there is voltage applied across the + dim/low/white/running light circuit.  They light amber when there is voltage applied across the + bright/bright/amber/turn signal circuit.

 

Basic Diagnostics:

 

1.  If your switch back bulbs are lighting up white, then there is voltage being applied to the + white contacts of the bulb by the system.

 

2.  If your switch back bulbs are lighting up amber, then there is voltage being applied to the + amber contacts of the bulb by the system.

3.  If your switch back bulbs are not lighting up, then there is no voltage being applied to either the + amber contacts or the + white contacts of the bulb by the system.

Basic Fix:

1.  To make the switchback led bulb light up white, apply 12 volts to the + white contact.

2.  To make the switchback led bulb light up amber, apply 12 volts to the + amber contact.  

3.  To make the switchback led bulb not light up, reduce voltage to less than 12 volts across the + amber and + white contacts.

How to determine if the bulb is faulty or the vehicle circuitry is just not functioning with the led bulbs in place.

Installing led bulbs are not always a "plug and play" operation.  Although we have devised our patented circuitry with as much logic as possible to allow it to plug and play in many vehicles, it is not possible to design the switchback bulbs to plug and play in 100% of all vehicles.

In order to properly diagnose and fix problems, it is essential to isolate bulb related problems from circuit related problems.   It is never a good idea to plug and led bulb into a vehicles circuit to test the led bulb.  This is testing both the led bulb and the circuit at the same time.  This method of testing will make it impossible to isolate problems with the bulb from problems with the circuit. 

It is always recommended that if the bulb is not working in the circuit, test the led bulb using two wires connected direct to battery or any other known 12 volt DC power source.  This is the only way an led bulb can be isolated from the circuit related problems and properly tested.

3157 white amber switchback  led conventional wiring schematic

How to fix circuit related problems.

OK you plugged your new led bulbs in and they "don't work".  The bulb must be defective, right?  WRONG!  

First... Did you test the bulbs as described above?  If not, you need to test the bulbs only.  Use the diagrams shown above to test the bulbs.  It is best to use two wires that are connected direct to battery to test the bulbs.  If you did not test the bulb as prescribed, you will never figure out if the problem is with the bulb or the circuit or the installation.  Never assume the bulb must be bad.  99.8% of the time, the led bulbs are working as they should, but the circuitry is just not set up to operate properly with an led bulb. The odds that you received a non-functional LED bulb is very unlikely....less that 1 in 500.

99% of the time, the circuit related issues can be overcome, but it may take some extra effort and/or some minor wiring changes to get the Switchback bulbs to work in some vehicles.

Here is a list of some common symptoms and fixes for automotive circuitry:

Symptom Fix
 I hear a buzzing noise from the bulb or radio.   One or more of the led bulbs is not secure in the socket.  Check the contacts on the bulbs and socket.  Realign or adjust as needed.  Reseat the bulb.
The 3157 led bulb causes a fuse to pop whenever I switch on the lights or when I switch on the turn signal.  As soon as I remove the led bulbs, the fuses do not pop.  You are using the conventionally wired 3157 led bulbs in a CK socket.  You can either swap the wires to the socket or use the specially wires CK led bulbsDon't forget to replace the fuse!
The glass filament style bulbs light fine, but the 3157 switchback led bulb will not light when I switch on the headlights. A.  The led bulb may be inserted backwards.  Remove the bulb, rotate 180 degrees and reinsert.

B.  The led bulb contacts may not be making solid electric contact with metal contacts in the socket.  Check the contacts on the bulbs and socket.  Realign or adjust as needed.  Reseat the bulb.

C.  Are you sure the filament bulb still works?  Often in the process of installing, you can pop a fuse or lose a wire/connection to the socket.  Always use the glass bulb or a voltage meter to verify there is at least +12 volts to the socket. 

D.  In some vehicles some automotive circuits will not fully energize the circuit, or pulse current to the bulbs to check to see if the bulb is burned out.  Since the leds draw 90% less power than the glass bulbs, these circuits do not switch on full voltage , or will not stay on when the led bulb is inserted.  This can be corrected by installing one 6 ohm load equalizer across the circuit at each led bulb.  This will add more load to the circuit and make the full 12 volt power switch on.   In this instance, the glass bulb will make the power switch on, but the led bulb by itself will not make the full 12 volts switch on.  

This creates the illusion that the led bulb is at fault when in fact there is not 12 volts at the connection when the led bulb is inserted.

The glass filament style bulbs work fine, but the 3157 switch back led bulb will not light when I switch on the turn signals. A.  The led bulb may be inserted backwards.  Remove the bulb, rotate 180 degrees and reinsert.

B.  The led bulb contacts may not be making solid electric contact with metal contacts in the socket.  Check the contacts on the bulbs and socket.  Realign or adjust as needed.  Reseat the bulb.

C.  Are you sure the filament bulb still works?  Often in the process of installing, you can pop a fuse or lose a wire/connection to the socket.  Always use the glass bulb or a voltage meter to verify there is at least +12 volts to the socket. 

D.  In some vehicles some automotive circuits will not fully energize the circuit, or pulse current to the bulbs to check to see if the bulb is burned out.  Since the leds draw 90% less power than the glass bulbs, these circuits do not switch on full voltage , or will not stay on when the led bulb is inserted.  This can be corrected by installing one 6 ohm load equalizer across the circuit at each led bulb.  This will add more load to the circuit and make the full 12 volt power switch on.   In this instance, the glass bulb will make the power switch on, but the led bulb by itself will not make the full 12 volts switch on.  

This creates the illusion that the led bulb is at fault when in fact there is not 12 volts at the connection when the led bulb is inserted.

The glass filament style bulbs work fine, but the led bulb will not blink or blinks rapidly when I switch on the turn signals.

With many flashers, led bulbs will cause the turns signals to flash rapidly, or not flash at all.  

If using led bulbs for turn signal applications, or in vehicles with bulb-out warning systems, like Mercedes, BMW and others, you may need to add load equalizers.    

For led turn signals, you can change the flasher out using one of our new patented combination led/oem bulb flashers.  Most electronic flashers are not the same as an led flasher.   Many electronic flashers do not necessarily work with led bulbs, unless they are led flashers.

If we do not have an led flasher that matches your flasher, use two 6 ohm equalizers for two front, or two rear led turn signal bulbs.

Place one load equalizer at each led turn signal bulb location.    For turn signal led bulbs, the equalizer must be spliced across the - ground wire and the + turn signal wire feeding each led bulb.

More details on load equalizers and led flashers can be found at:    

http://www.autolumination.com/equalizers.htm

The switchback bulbs are lighting up amber when the headlights are on and the turn signal and emergency flashers are off. 

A. You may be using a 3157 switchback bulb in a 3156 socket.  Check to see how many wires there are going to the bulb socket.  If there are only two wires going to the socket, then it is a 3156 socket and the 3157 bulbs will not work in a 3156 socket.  

B.  There is voltage being applied to the + amber contacts of the bulb by the system.  Determine the source and correct as needed.

The switchback bulbs are flashing amber- off-amber-off when the lights are off and flashing amber white-amber white when the lights are on.   AW - Amber - White Switchbacks

The Amber -White (AW) Switchback bulb has special circuitry inside that senses when there is voltage on the (amber) turn signal circuit.  Whenever there is voltage on the (amber) turn signal circuit, the bulb switches to amber mode.  The result is that in most vehicles, the AW switchback will flash amber-off-amber off whenever the turn signal is activated and the headlights/running lights are off and amber-white-amber-white whenever the turn signal is activated and the headlights are on. the switch back bulb will flash amber-white-amber-white,  whenever the turn signal is activated and the headlights are on. 

In some vehicles, the power to the (white) running light circuit is automatically switched off whenever the turn signal is activated.  In these cases, the AW switchback will flash amber-off-amber off whenever the turn signal is activated.

   

Note:  There are two styles of switchback bulbs:

 1.  AO - Amber - Off

2.  AW - Amber - White

Operational description Animation

AO - Amber - Off

The Amber -Off (AO) Switchback bulb has special circuitry inside that senses when there is voltage on the (amber) turn signal circuit.  Whenever there is voltage on the (amber) turn signal circuit, the bulb switches off power to the (white) running light circuit for 2 seconds.  The result is that in most vehicles, the switch back bulb will flash amber-off-amber off whenever the turn signal is activated, even when there is power to the (white) running light circuit.

The bulb will switchback to white if the headlights are switched on and the turn signal circuit is switched off for 2 seconds. 

The bulb will switchback to off if the headlights are switched off and the turn signal circuit is switched off for 2 seconds. 

The result (in most vehicles) is shown in this animation with the headlights on.

Switchback led bulbs white amber turn signal bulb

AW - Amber - White

The Amber -White (AW) Switchback bulb has special circuitry inside that senses when there is voltage on the (amber) turn signal circuit.  Whenever there is voltage on the (amber) turn signal circuit, the bulb switches to amber mode.  The result is that in most vehicles, the switch back bulb will flash amber-white-amber-white,  whenever the turn signal is activated and the headlights are on. 

In some vehicles, the power to the (white) running light circuit is automatically switched off whenever the turn signal is activated.  In these cases, the AW switchback will flash amber-off-amber off whenever the turn signal is activated.

In most vehicles, the AW switchback will flash amber-off-amber off whenever the turn signal is activated and the headlights/running lights are off..

The AW switch back bulb as it will operate (in most vehicles) is shown in this animation with the headlights on.

Switchback led bulb white amber turn signal bulb


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