Disclaimer
I'm sorry to say that I must include the following disclaimer. You accept full responsibility for performing these mods on your car. While these instructions are accurate to the best of my knowledge, I cannot be held responsible for any errors that they may contain. I also cannot be held responsible for any ill effects due causes including, but not limited to the following:- Improper following of instructions
- Errors in the instructions
- Differences in your vehicle from mine
- Any other cause
Goal of the Mod
The goal of this mod is to modify the behavior of the side marker lamps in the front fenders of North-American-spec cars. Currently those lamps are lit with the parking lights. The desired behavior is to continue to have them light with the parking lights, but also to have them blink with the turn signals. Specifically, the new behavior will be as follows:- When the parking lights are off, the side marker will normally also be off. The exception is that when the turn signals are in use while the parking lights are off, the side marker light will flash in sync with the turn signal bulb on that side of the car.
- When the parking lights are lit, the side marker will also normally be lit. The exception is that when the turn signals are in use while the parking lights are lit, the side marker light will flash the opposite polarity to the turn signal bulb on that side of the car.
Wiring Overview
Currently the lamps in question are wired with one terminal connected to ground, and the other to switched 12V. In the case of the turn signal lamp, the switch is the turn signal blinker and switch; in the case of the parking and side marker lights, the switch is the headlight switch. Check out the simplified diagram below for details.
The change, which is also noted in the diagram above, is to lift the side marker lamp's ground connection and instead hook it up to the switched side of the turn signal lamp. FYI in VWs ground wires are always brown, but sometimes have a stripe of another color on them. The turn signal and the parking lights will still be wired as before (one side switched 12V, the other side ground). However the side marker lamp will now be connected between the switched 12V going to the turn signal lamp, and the switched 12V going to the parking lamps.
How It Works
To show the functionality of the mod, we'll have to consider a few different cases. Note that in these cases, when it is noted that the "turn signal is off", that means that the bulb is not illuminated. This might mean that either the turn signal switch is off, or that it is on but the blinker is in the half-cycle where the bulb is not to be illuminated. Likewise, "turn signal on" means that both the switch is on, and that the blinker is in the half-cycle where the bulb is to be illuminated:Case 1: Parking lamps off, turn signal off. In this case both switched 12V signals (parking and turn) are at 0V since no power is applied to either. All of turn signal, parking, and side marker are off.
Case 2: Parking on, turn signal off. In this case there is 12V applied to the top of the parking lamp and the top of the side marker lamp. In looking at the simplified schematic above, you'll note that there is a complete circuit from 12V, through the side marker lamp, through the turn signal bulb, to ground. So on first thought, both the turn signal and the side marker lamp will light at half-brightness.
However this is where we depend on the fact that the side marker lamp is much smaller wattage, and therefore higher-resistance than the turn signal lamp. If we have a voltage divider with two resistors, most of the voltage will appear across the higher-valued resistor (in this case, the side marker lamp).
The second thing we depend upon is that incandescent lamps are by nature non-linear resistors. When the filament is cold, its resistance is much lower than when it is hot. So, by the principle above the side marker filament will get hotter than the turn signal filament, which will accentuate the differences in resistance. The effect is that the side marker bulb will glow at close to 100% of its full intensity, while the turn signal bulb will not glow at all.
Therefore in Case #2, the parking lights and side markers will be on, while the turn signal will be off. This is the effect we want.
Case 3: Parking lamps off, turn signal on. In this case there is 12V applied to the top of the turn signal (and therefore the bottom of the side marker lamp). In looking again at the simplified schematic above, you'll note that there is a complete circuit from 12V, through the side marker lamp, through the parking lamp, to ground. The same principle as noted above will be in effect here: even though the side marker and the parking lamp are in series, only the side marker bulb will illuminate. Therefore in this case, the turn signal and side markers will be on, while the parking lamp will be off.
Case 4: Parking lamps on, turn signal on. In this case there is 12V applied to both sides of the side marker light, so no current will flow and the bulb will be off. In this case, the turn signal and the parking light will be on, while the side marker will be off.
Results
So here is this overall effect:- When the parking lights are off, the side marker will blink in sync with the turn signal bulb.
- When the parking lights are on, the side marker will be illuminated while the turn signal bulb is not illuminated, and the side marker will be extinguished when the turn signal bulb is on. Therefore it will also flash while the turn signal is flashing, but it will flash the opposite polarity.
Procedure
Don't forget to check out the disclaimer before proceeding. I also recommend that you fully read the instructions before you proceed in order to familiarize yourself with the process.Parts required:
- Radio Shack Catalog # 64-3067 (Moisture-resistant tap-in connectors; qty 4; for 18-16 gauge wire; only 2 used in this operation)
And here's the procedure.
- If you have a Bentley manual handy, I strongly recommend that you
check out the wiring diagram to double-check my color codes. In my
Bentley the appropriate diagram is on Page 97-237.
- I've found it easiest to do this with the headlights removed. To
get them out, you'll unfortunately first have to remove the grill. To
the best of my recollection, here's how you do it. Be very
careful when removing the grill; I've already broken off two of the
tabs that hold in mine.
- Remove the four phillips-head screws that go through the top radiator support down into the top of the grill.
- Carefully press down on the four plastic clips in the grill which the screws held. Gently disengage the top of the grill from the top radiator support.
- Use a screwdriver to carefully press the five or so plastic tabs that hold the bottom of the grill in. Gently disengage the bottom of the grill from above the bumper, and lift out the grill.
- Using an 8mm socket, remove the four screws from each of the headlight assemblies; disconnect the headlight wires and set the headlight asssemblies aside.
- For the purposes of this procedure, the notations of the
left and right sides of the car are from the point of
view of a person sitting in the driver's seat. Therfore the
left side of the car is the driver's side (on North American
spec cars, anyway).
- Start on the "Driver's Left" side since there's more room to work
(at least on my early '96). Locate the wiring harness that runs below
and inside the headlight opening. It will be wrapped in black tape.
If you follow the outboard end it will split and feed the side marker
lamp, and the turn/parking lamps in the front bumper.
- Using an exacto knife or other cutting implement, gently slice
away a 1.5-inch-long section of the black tape in the harness just
below the headlight opening. Be careful not to cut or puncture the
insulation of the wires inside!
- As a test, turn on the parking lights to make sure both side
marker lights illuminate. Turn them off again.
- Check out the diagram below. Locate the thin brown wire (there
may be a stripe on it) in the harness. Be sure you identify the
thin brown wire. Don't confuse it with the fat brown
wire. Cut the thin brown wire at the inboard-end of the gap in the
black tape. Turn on the parking lights to verify that the side marker
light on this side of the car does not illuminate. This will
verify that you've cut the correct brown wire. Note! Some
people who have done this mode have reported that their cars have
two fat brown wires, but only one thin brown wire. As
long as you only have one thin brown wire, that's the one you want.
If you have more than one, I can't help you with which one to cut.
- Important! When connecting the thin brown wire to the tap-in
connector, make sure you connect the half that runs toward the
outboard edge of the car, toward the side marker lamp! Do not connect
to the half that runs inboard, to the wiring harness, and eventually
to ground! If you connect to the wrong half, not only will the mod
not work, it will also blow fuses (or worse) when you energize the
turn signal. Double-check the
schematic and the
diagram
above to make sure you get the correct half.
- Locate the thick black/white wire. Apply this wire to the Tap-in
Connector's "through wire" position. Be sure to have the Tap-in
connector's "tap wire" position pointing toward the outboard edge of
the car (to accept the longer end of the cut brown wire). Apply the
longer end of the cut brown wire (the end which runs toward the side
marker lamp) to the "tap wire" position. Close and lock the
connector.
- Turn on the parking lights. Verify that the side marker light on
this side of the car does illuminate. Turn on the emergency
flashers. Verify that the side marker light flashes. Turn off the
parking lights and flashers. You're done
with the Driver's (left) side. Now move to the Passenger's (right)
side. Locate the harness on this side of the car and carefully cut
another 1.5-inch-long opening in the black tape wrap.
- Check out the diagram below. Note! Owners of non-1996 cars have
noted that there may be more wires in this bundle than I've shown.
Locate the thin brown wire (there may be a stripe on it) in the
harness. Again, be sure you identify the thin brown wire.
Don't confuse it with the fat brown wire. Cut the thin brown wire
at the inboard-end of the gap in the black tape. Turn on the parking
lights to verify that the side marker light on this side of the car
does not illuminate. This will verify that you've cut the
correct brown wire. Note! Some people who have done this mode
have reported that their cars have two fat brown wires, but
only one thin brown wire. As long as you only have one thin
brown wire, that's the one you want. If you have more than one, I
can't help you with which one to cut.
- Again, it's important that you connect the half of the thin
brown wire that runs toward the outboard edge of the car, toward the
side marker lamp! Double-check the
schematic and the
diagram
above to make sure.
- Locate the thick green/black wire. Apply this wire to the Tap-in
Connector's "through wire" position. Be sure to have the Tap-in
connector's "tap wire" position pointing toward the outboard edge of
the car (to accept the longer end of the cut brown wire). Apply the
longer end of the cut brown wire (the end which runs toward the side
marker lamp) to the "tap wire" position. Close and lock the
connector.
- Turn on the parking lights. Verify that the side marker light on
this side of the car does illuminate. Turn on the emergency
flashers. Verify that the side marker light flashes. Turn off the
parking lights and flashers. You're done with the Passenger's (right)
side.
- Re-install the headlight assemblies and the grill. You're done!