Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2004 300M headlight problem

My 300M’s headlights will flash on and off on their own. When this happens the entire headlight system (head, tail, dash) flash. I replaced the realy but no joy. Could the auto light feature be competing with the headlight switch? Is there a way ot disable the auto function, we don’t use it anyway. This happens in broad daylight and so far has not occurred at night. We always drive with our lights on so I would think that having the switch ion the on position would by default disable the auto function.

I would guess the trouble is either with the light switch or in the power line to it. Testing at the input to the switch would be the first step I would say.

If you turn the switch to the right instead of the left (not to “A”), the auto light feature is disabled, and the switch is a manual headlight switch with two positions–parking lights and headlights. On many cars (not sure how yours is wired), there is a circuit breaker built into the headlight switch. When they get weak from long use (or there’s a genuine overload), the breaker heats up and disconnects the circuit. Then it cools and the lights come back on again. This can happen rapidly enough to make the lights flash. It may be that it’s hotter during the day when you drive it, and this makes the breaker more sensitive, especially on a warm day if you don’t use the A/C. If you drive with your lights on all the time, that’s certainly more use than most get, and it could be a weak circuit breaker.

If you can get it to happen at night, try switching it to auto and see if the problem persists. I think when the lights are set on manual, more current runs through the switch, while on auto, a relay handles much of the current, and it may be fused separately instead of using the breaker built into the switch. (if yours has it built in) Again, I’m not sure how this is wired, so a wiring diagram may answer all your questions.

I’m not certain as to whether this is what’s happening in your situation, but it’s my best guess. Why do you drive with your lights on all the time?

Where is your sensor located, mine a different brand is located in the middle of the dashboard near the window. Is it possible something is sliding over it masking it think it is night time?