Left Parking Filament and Turn Filament ON when headlights ON, 1987 BMW 325e

[spencerhitch]

Hello,

If you've got any suggestions for the following issue I would be incredibly grateful. I'm new to working on cars and this electrical issue has got me stumped! My best guess is that some wires are crossed/shorted in the front left fender/lighting area, that are running the ground through the entirety of the lighting system!

Funky behavior:
CASE 1: headlight switch OFF => turn signals function at normal rate, left front signal is more dim than right. Turn indicators show in dash.
CASE 2: headlight switch ON => right parking filament ON, right turn filament functions normally with control. left parking filament ON, left turn filament ON (non-flashing), left indicator in dash ON (non-flashing).

Things I've tried:
1. Test continuity (resistance) to body of car => every wire (not just brown) in headlights and turn lights has continuity to body of the car!
2. left front bulb and right front bulb switched => same behavior as CASE 1 and CASE 2
3. left front bulb removed => everything works as it should, back left turn signal blinks twice as fast as normal.
4. clean ground connection at front left fender. => no change

Relevant history:
1. Previous owner had removed all turning bulbs, had never noticed odd behavior with headlights ON
2. I had first noticed behavior after installing turning bulbs AND replacing turn signal control at steering column.

Please help me bimmer forums!

- - - Updated - - -

Relevant wiring diagrams:
http://imgur.com/a/VQSoy

[richardodn]

Check the lamp socket and connector behind the fixture for corrosion.

[Uturn540]

You have a defective left bulb. The bright(turn) element is probably broken on the ground side and the broken end is touching the hot side of the dim(parking) side. With the parking lamps off the turn signal element is grounding through the parking element. The parking element will only let enough current through to illuminate itself and not the brighter turn element therefore only the dim parking element will illuminate and flash. When the parking lights are on the parking element is constantly illuminated and therefore will not blink even though the bright element is trying to feed power through it.

[spencerhitch]

@richardodn I originally thought the socket might be corroded but it seems to have all the same behavior as the right socket. Here is a photo of what the socket looks like with the bulb removed, doesn't look corroded to me. If I want to take the enclosure out I have to remove the entire bumper?

@Uturn540, all of that would make total sense but if the bulb is defective then why is it that when I switch the left bulb with the right bulb the left side is still the side that misbehaves?

[Uturn540]

I looked at your original post and the wiring diagram. The only thing I can figure is a bad ground. Try running another wire from the point where the lamp assemblies ground to the engine block. It looks like the original ground is on the inner fender and that itself may not have good continuity to the rest of the vehicle.

[spencerhitch]

I've lived with this for 3 years. The problem is intermittent. I can get the light to work properly if I reach in, by hand, and fiddle with the wires leading into the bulb, straightening them etc. That usually resolves it for about a month.