Flashing Side Marker Lamps

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Most 1968 and newer (and all 1970 and newer) vehicles first sold in the USA or Canada are equipped with amber front and red rear side marker lights. These are intended to show the presence, position, and direction of travel of the vehicle after dark. They do that job very effectively. But there's no requirement in North American lighting regulations for side-on visibility of vehicle turn signals. Some vehicles have turn signal repeaters mounted on the front fenders or side view mirrors as required in most countries outside North America. Adding repeaters to a vehicle not originally equipped requires drilling holes and adding new wires, which presents issues with vehicle body rust and body shop costs. The front side markers are allowed to flash with the turn signals, but it's not required. There's a video below showing a vehicle set up with flashing front side marker lights. Having them flash is an advantage, because that way your intent to turn or change lanes is visible to drivers who are alongside your car and cannot see your front or rear indicators—as well as to pedestrians, bicyclists, and others who have a personal interest in not trying to occupy the same space at the same time as your vehicle. There are several methods for adding flashing functionality to side marker lights. Some of these methods are suitable for only certain kinds of lights, and those will be discussed below; we'll start off with the method that works on every vehicle no matter what kind of side marker light or circuit it might have.

Module method: Works on any vehicle

pick up a DRL-1 module for $63. Send me an email to order. This durable, dependable, compact, self-contained logic circuit works perfectly to control the front side markers so they do double duty as both steady-burning side markers and as side turn signal repeaters. You need only one module to do the whole job, there's no underhood clicking or excessive parts count as with the relay method, no tedious ground isolation needed, and it works with any kind of side marker light. One-wire, two-wire, filament bulb, LED...doesn't matter. Some late-model vehicles—even those with ordinary filament bulbs for the side markers—have body computers that don't look favorably on the basic wire mod as described above. For these situations, too, the DRL-1 module is the quick and clean fix.

If you do it this way, the side markers will always flash in synchronous phase with the front and rear turn signals, whether the parking or headlamps are on or off. They will not flash in opposite phase when the parking or headlamps are lit, as occurs with the other methods described below. Either mode is acceptable in North America; most other countries do not allow side markers to flash in opposite phase, so the DRL-1 module is the only acceptable solution when importing an American-specification vehicle to a country that uses the international European auto safety standards; this method will in many cases satisfy the requirement (which does not exist in North America) for side turn signal repeater functionality, without giving up the side marker functionality. The obverse is also true: if you're bringing a European-, Japanese-, Australian-, or other-spec vehicle into North America and have to have a front side marker function, this method lets you add it via the existing repeaters (if they're acceptably close to the front of the vehicle) without giving up the side repeater function.

To hook up the DRL-1 module as a side marker controller, connect the wires as follows:

Neatly tape off and secure unused wires and cut ends (such as the non-lamp, "vehicle" ends of the two cut side marker feed wires, and the unused blue and white wires on the DRL-1 module). For tapping into existing circuits in a good and durable manner, I am a great fan of Posi-Tap connectors as described here, available from the manufacturer here and increasingly available locally. You can also use crunch-type circuit taps (e.g., ScotchLock); if you go this route be sure to use good quality ones.

Crossfeed method

Vehicles with 2-wire, bulb-type side markers have come from the factory two ways: with the front side marker bulbs wired across parking lamp feed and turn signal feed, which provides a flashing side marker, or wired across parking lamp feed and ground, which results in a non-flashing side marker. There's no rhyme, reason, or consistency to which vehicles have what; front side markers may flash with the turn signals, but they're not required to, so it's a matter of automaker whim; the Jeep Wrangler had flashing front side markers until 2004, non-flashing starting in 2005. It's pretty random and arbitrary. If your vehicle has two-wire front side markers with filament bulbs, and they don't flash with the turn signals, you can make them do so by moving one wire.

Here's how the front parking, turn signal and side marker lights are wired so the side markers do not flash:

This diagram shows the common "park/turn" bulbs, with a bright turn signal filament and a dim parking lamp filament in the one bulb. Each filament has its own feed terminal on the bulb base. The wiring is the same in systems that have separate bulbs for the parking lamp and the turn signal; the only difference is that the park lamp feed and the turn signal feed go to separate bulbs.

With this hookup, the side marker lamps are wired exactly like the parking lamps. They are always grounded, and they receive +12V whenever the parking lamps are on. Therefore, they illuminate steadily whenever the parking lamps are on, and never flash.

Here's how the system is wired to make the front side markers do double duty as side turn signal flashers:

There's only one difference between this setup and the non-flashing one: Instead of the side markers being wired across parking lamp feed and ground, they're wired across parking lamp feed and turn signal feed.

The side marker bulb socket is isolated from ground, and one bulb lead goes to the running lamp positive circuit. The other lead is tied into the turn signal positive lead.

When the parking lights are on and the turn signal off, it grounds throught the turn signal filament and illuminates the marker lamp. When the turn signal flashes, it interrupts the ground and the marker will flash. When the running lights are off, the process is reversed, with the ground being through the filaments of the running light circuit, and the marker will flash in sync with the turn signal instead of alternately.

Here is a video showing the results of this modification on a Ferrari 328GTS. First with the parking lamps off, then with them on:

Why does this work? Because of the difference in wattage between the side marker filament (3 to 6 watts) and the turn signal filament (21 to 29 watts). There are at least two turn signal filaments—at least one front, at least one rear—through which for the single side marker filament to ground when the turn signals aren't lit. As far as the low-wattage side marker filament is concerned, the high-wattage turn signal filaments look like a low-resistance path to ground; the low-wattage side marker doesn't send enough current through the turn signal filaments to light them up.

1-wire and LED side markers

The move-one-wire method won't work if your side markers use LEDs rather than filament bulbs, or if they have only one wire and get their ground through the mounting of the lamp housing to the body sheetmetal rather than via an actual ground wire.

If you have single-wire, body-grounded side markers, there are three ways to achieve flashing side markers. To do it the hard way, you must well and thoroughly isolate and insulate the side marker housing from ground, then attach a ground wire and proceed as described above. Materials and supplies useful in isolating and insulating body-ground side markers include nylon mounting hardware rather than metal, rubber gasket material, liquid electrical tape (in the brush-top can), and the "Plasti-Dip" material available at hardware stores for creating insulating flexible plastic handles on bare metal tools. But take a careful look at your side markers and how they mount to make absolutely sure you can achieve a good and durable insulation from ground. If your insulation job fails, you'll have a short circuit which will blow the fuse and kill the lights (or cause worse damage if you're less fortunate).

Likewise, the basic modification as described above will not work with front turn signals and/or side markers that use an LED light source rather than a filament bulb. That's because the modification depends on current flowing with equal ease and effect in either direction through the light source. That's true of a filament, but not of a light-emitting diode (LED).

With single-wire/body-ground or LED side markers, A workable method is to put a relay in the feed wire to each front side marker. Parts count is kind of high to do it this way—two relays, each with its associated fuse, fuse holder, terminals, relay mounting block, etc. And you may find the resultant relay clicking under the hood to be creepy or irritating if that sort of thing bothers you (though you're unlikely to hear it from inside the car). Nevertheless, if you want to do it this way, wire an ordinary normally-open ("NO") 4-terminal relay in on each side of the car as follows:

Relay terminal 85: to vehicle end of cut side marker feed wire
Relay terminal 86: to vehicle end of turn signal feed wire via splice
(with Posi-Tap connector as linked above)
Relay terminal 30: to always-hot +12v via a fuse
Relay terminal 87: to side marker light end of cut side marker feed wire

It's easier to use the module method.

Daniel Stern Lighting (Daniel J. Stern, Proprietor)

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Copyright ©2011 Daniel J. Stern. Latest revisions July 2019. No part of this text may be reproduced in any form without express permission of author. Permission to quote is granted for the purposes of communication with the author.