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NOTES:
There are five things to keep in mind.

1. LED swaps for the H4 (and others) headlight bulb are illegal in many jurisdictions. They may look great as the driver but they are horrific for oncoming traffic or cars you are following. Regulations stipulate that LED main driving lights are to have self leveling and or self cleaning technology which is incorporated into modern cars with LEDs. This keeps the beam pattern low and it’s very obvious in modern cars. Old style reflector type headlights like on the W124 spray too much light at oncoming traffic even with the best H4 LED designs. The problem is the reflector and the inherent brightness of an LED. Keep this in mind. You can make the park lights LEDs (located inside the headlight housing on W124’s) and that looks awesome as it gives a white/blue glow to your headlights without impacting oncoming traffic. This also makes excellent daytime lighting.

2. W124’s have a bulb failure warning system. It is in the Lighting and Illumination control module (N7 on the circuit diagram). LEDs on any location monitored by the module will flag a failed bulb as the LED draws so little current the module thinks the bulb has failed. This will produce a bulb warning light on your instrument cluster and also means if a bulb actually fails, you won’t know if it has or not.

3. The same low current draw as above will cause the Indicator/Signal control module to think a signal/indicator bulb has failed and cause it to ‘Hyperflash’ (flash at twice the normal rate) which lets you know a signal bulb has failed. Unless you want to play with cutting and soldering new resistors into the Indicator control module it will be best to leave indicator bulbs as EOM for now. But it can be done. Follow this link here to lean how on YouTube.

4. The Alternator Failure warning light (looks like a battery) is part of the alternator excite circuit. A failed bulb will not allow the alternator to excite so the alternator will not charge the car battery. An LED inserted in the alternator warning section does not draw the necessary 0.5 Amps minimum to excite the alternator so you will need to either leave the original OEM bulb (working) in that location or add in an inline resistor to provide the 0.5 Amp current draw.

5. Every effort has been made to check and cross check the validity of the codes and links. Investigate carefully and check against your old bulbs to determine you have the correct bulb if you choose to purchase.