How To: Installing Led Bulbs For Sequential Tail Lights

Discussion in 'SN95 V6 Mustang Tech' started by StarbuckSapien, Jun 3, 2013.

  1. Summary: To use LED 3157 tail light bulbs you must install at least one resister per light assembly.

    I had purchased a sequential tail light kit and I liked the uniqueness of the light sequencing but I felt that it reduced safety a bit. I felt that way because the brake lights are also sequenced, in addition to the turn signals, and that means when you first step on the brake you only get two bulbs out of six lighting up. I wanted to get the lights started faster so I purchased LED bulbs that fit directly into the 3157 bulb sockets. I did not go with an LED tail light assembly because (at this time) those are not compatible with the tail light sequencing harness. I could not find any detailed info on this when I was planning the project, so I’m documenting my experience here.

    The Install:
    I purchased 6 dual-intensity red 3157 bulbs with 45 LEDs on each bulb (part number 3157-x45-T). The sequential light harness was already installed, so I simply installed the bulbs in place of the existing filament bulbs. Subjectively, the LED bulbs appear brighter than the filament bulbs, and they light up immediately, so I was very happy with that result.

    However, as expected, with the LED bulbs installed the Mustang’s electrical system thought that a bulb was burned out and when using the turn signal it would fast-flash. I had purchased a Raxiom flasher to slow down the signal sequencing, and I hoped that would eliminate the fast-flash when I installed it, but it did not. So I knew I had to install resistors to make the system think that filament bulbs were installed.

    I purchased the resistors from the same place where I got the bulbs ( and was pretty happy with what I received. Each resistor comes with two vampire clamps already filled with dielectric grease. I went to Ace Hardware and picked up two #4 3/8” sheet metal screws, two rubber washers, and a rubber cork for each resistor.


    The documentation on the resistors says that they get hot and should not be attached to plastic, so I drilled into the sheet metal (5/64” bit) behind the light assembly and attached it as shown in this picture. You can use this same relative location for both assemblies. I installed the rubber washers under the resistor to help prevent rust. The sheet metal screws stick out into the trunk, so I cut the rubber cork in half and used those to prevent future injuries to me! I drilled a hole into the two rubber cork parts and screwed each onto the exposed portion of the sheet metal screws.

    The general information on the web states that you need a resistor for each LED bulb, but I discovered that in my installation that is not accurate. I installed one resistor on the wire to the bulb that is the first one in the sequence to light (inner-most bulb). That one resistor appears to be enough to convince the electrical system that there are no burned-out bulbs. It does not matter which end of the resistor is connected to the ground (black) wire and which one is connected to the hot wire.

    The final result is that I have bulbs that are brighter and light up faster and have eliminated the fast-flash problem. I am very happy with the result.

    Full disclosure:
    Okay, on the first assembly I installed three resistors. I did not think to try only one until I started on the passenger side. While I was in there, I also installed part number 3156-x45-T on each side to replace the reverse lamp bulbs.
  2. You can safely ignore all of this now, because American Muscle has a kit that includes everything and is a lot cheaper than my install was.