E28 MOD - Rewire Side Marker Lights as "Auxiliary Turn Indicators"

A few weeks back there was some dialogue on the digest about adding the "Auxiliary Side Turn Indicators" to some cars that did not have them. The additional indicator can be a helpful safety feature, especially on those E28’s with the North American style bumpers where the parking/turn signal could not be seen from the side.

Many of you already have these, and on many others the front "side marker light" flashes, with the turn indicator, to provide the same functionality.

BUT
The early E28’s, and other models of that era, did not have that feature. On those, the side marker light simply lights with the parking lights.

If anyone wants to have them also "flash", with the turn indicators, the following mod will do the trick.

MOD FUNCTIONAL DESCRIPTION
Description is based on 82 528e model. Others are similar, but there may be differences.
This mod re-routes the "ground" connection for the front side marker lights. It disconnects it from the body ground, and connects it in parallel with the hot side of the front turn indicator bulb.

Function - with parking lights "on".
This still allows it to operate as a marker light, but it now gets it’s ground "through" the turn signal bulb, which does not light since it is a 21 watt bulb and the marker bulb is only 5 watt. But - when the turn signals flash "on", this removes the ground for the side marker lamp, and they flash "off" - thus the two bulbs both flash, but in opposite phase.

Function - with parking lights "off".
In this case the side marker will flash "in phase" with the directional indicators
The flashing circuit applies "battery" on the side of the marker lamp that used to be the ground. Therefore it needs a ground on the other side, which is the hot wire for the parking light. Since the parking light circuit is off, there is no battery there , but there is ground available "through" the front & rear parking light bulbs. In this case the parking light bulbs are of similar capacity as the marker light (5 watt), but since the front and rear parking lights are wired in parallel, they are the electrical equivalent of a single 10 watt bulb, and therefore provide adequate ground capacity for the 5 watt side marker.

Note: this will not affect the operation of the rear light check function.

DEGREE OF DIFFICULTY:
This is a simple mod - DOD 3/10

REQUIREMENTS:
Wire cutters, soldering gun/solder, electrical tape.

PROCCEDURE

1. The front side marker lights are grounded with brown wires. They are connected, with many others, to a body ground connection on the inside of each front fender. Trace the brown lead from each front marker lamp, and cut it just at the body ground connection. Strip back the insulation ¼ inch.
2. You now need to locate the "hot" wires going to front turn signal lamps, on each side of the car. They are accessible by cutting into the plastic wire harness, inside the front fender on each side. To make this as easy as possible, choose a spot close to where you cut the ground wire from the marker light, so that it will reach. The wires you require are:
   • Left (drivers) side - blue/red
   • Right side - blue/black If your car is not an E28, you may want to verify the colours by looking at the rear of each front turn signal lamp socket.
3. Do not cut these wires but rather strip a short piece of insulation off each. Connect the "cut" brown ground wire from each of the side marker lamps. Solder, and insulate with electrical tape.
4. Test:
   • marker lamps should still come on with parking lamps.
   • marker lamps should flash as directional signals with parking lamps on, or off (remember they will work in different phases)
5. All OK ? - Tape up the incision you made in the wiring harness.

Dat’s it - Eh !

Happy Signalling in the New Year.

Cheers

Jim Cash
London, Ontario, Canada
BMW CCA 102929
E39 97 540iA