Hello All,
This is the first thread that I've generated. I have owned my 2004 boxster for a little over a year now and absolutely love the car. I can't believe the local police have not locked me up yet. Anyways, I've recently noticed that my driver's side headlight is not working properly. The low beam setting is where I'm having the problem. When the parking lights are turned on, both headlights come on and are the same brightness, but when the headlights are switched to the on position only the passenger headlight comes on. The driver's headlight remains dim. Both headlight work properly when the high beams are switched on. I've changed the low bean bulb in that headlight but it did not fix the problem.
From your description I'm guessing you have DRL's on the car which use the low beam? If so my suspision is that the circuit that switches from the lower power (voltage) daytime setting to full voltage isn't working. No idea if this is handled solid state in the Boxster or just a relay or if there's a fuse in the circuit on both legs.
You could confirm this by comparing voltage supplied to the low beam from right to left. Both should go to 12 Vdc if working correctly when the lights are switched on.
Way back when Porsche had a central electric box the relays were marked along with the fuses. Don't know if that the case in '04 or not. If so you might be able to find the offending part. In the newer Cayman's the relays are scattered all over it seems.
It's also possible that the parking lights are illuminating a different bulb entirely. If so you would want to start checking the fuse panel. Low beam should be marked.
Well, Let me tell you what I found out when I did some testing today. I pulled the passenger side headlight and measured the voltage at the headlight connection. I tested the connection in several states; parking lights on with no key, parking lights on with the key turned to the on position, low beams turned on with the key in the same position as previously stated, high beams on with key...., side marker lights turned on with key ..... All voltage/ohm reading were identical in both circuits under all conditions. I then switched the low beam bulbs between the two headlight units. The driver side problem continued to persist with the passenger side bulb and the driver side bulb worked correctly in the passenger side headlight unit. I'm baffled. Identical conditions exist in both headlight circuits and headlight units, however one works while the other does not. I'm wondering if a relay could cause this or maybe the connection is the culprit. I haven't a clue how I'd test the connection due to the engineering of the headlight and the circuit involved. I think I'll have to remove the front fenders to gain access to these connections. Thanks for the insight though.
How are the headlights illuminated with the parking lights? Do you mean fog lights?
Jam, maybe I just can't read but it looks like you did all the measuring on the passenger side. Did you measure the driver side? With the key on and low beams turned on the bulb should be getting around 12 V between the low beam + to the ground connector on the bulb socket. This is what I suspect you measured on the passenger side.
And yes a corroded or loose connector or bad ground strap can cause this. I really don't think it's a bulb problem.
I can only give you hints at what to look for. But if you are changing bulbs you should have access to the socket you need to check voltage on to check the drivers side. These are halogens yes? Not Litronic?
