(Solved) Baffled with unexplained fog light problem.

[dsphil]

My driver side fog light has a strange problem.

I can not get a bulb that would light up on the driver side.

I have diagnosed the following; with wiring diagram.
-Checked the fuses before and after. Swapping fuses left and right. No blown fuses.
-Connect the bulbs with the lens and without the lens.
-Check with meter and circuit testor at the connectors with consistant voltage as other side.
-Swap bulbs with other side and the bulbs are fine.
-Connect to a 12v computer fan and it works. Checked the current also.
-Connect a bulb to it and it don't work.
-Connect the same bulb to other side and works.
-Check the polarity is fine.
-Tried different bulbs with no luck.
-Check the currents on both side and both sides draw 5 amps which is consistant for a 55w bulb give at about 12v.

You would think as long as I got voltage, the bulb would light up. Not in this case.

[Stanley Rockafella]

I had a flickering fog light on my drivers side of the e30.

I never tried nearly as many things as you, but I did pack a little dielectric grease into the socket of the plug that goes to the connection on the blub.

Since then the light has performed fantastically. Never missing a beat!

[ELVA164]

Sounds like something is wrong with the light itself, either in the plug or maybe some sort of internal ground issue. You swap the actual lights side to side, not just the bulbs?

[dsphil]

Sounds like something is wrong with the light itself, either in the plug or maybe some sort of internal ground issue. You swap the actual lights side to side, not just the bulbs?

I have swap both the lights itself and just connect the bulbs directly to the connectors as well. I also isolated the working side by pulling the fuse. Like mentioned, i put a 12v computer fan to it and it spins.

Drawing 5 amps


12v power

[IceWhite]

After looking at those pics above, the only thing I can think of is to maybe crimp those lugs tighter for a solid connection.

Hope that helps if you haven't tried it already.

[cirrusblue]

Check for a short once its all jammed in the box


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[AndrewBird]

11.89v would make the battery DEAD. A fully charged battery will read just under 13v. I'd say there is a short or something on that side that is pulling the voltage down and causing the bulb to not light. If you measure the battery directly, how many volts does it show?

[dsphil]

The engine is not running when I am doing this and the headlights and 1 of the fog is on. It is drawing power quite fast. The battery just replaced couple weeks ago. The same bulb will light up with a 9v battery. If there is a short, I would expect the fuse to blow. I didn't measure the battery voltage, I measured both sides and it is the same.
Anyways, something worst happened today to the working side. I forgot to screw it back on yesterday. This morning it fell off as I was in the highway and I ran over it.

[Das Delfin]

My inclination is the wiring leading to the bulb must be corroded, resulting in higher than acceptable resistance along the wire. It would accommodate for the reduced voltage as well as the reduced current supplied to the bulb (reason why it will power a comp fan but not a 55w light)

You can check this with an ammeter and your fuse box. Pull fuses one at a time and double check to make sure each circuit isn't pulling an obscene amount of current. When you get to the drivers side fog light compare it to the passenger; if they are radically different there's your answer.

You can do this without the light installed :P

[ELVA164]

Sorry to hear about your other light :(

[dsphil]

Solved

After endless diagnose, it finally comes down to the connector harness. Yes, little corrosion can ruined it. When I check the connector harness and the leads to the light, everything looks ok until it was plugged it. I used one wire at a time and concluded that there was a problem with the ground lead.

So a little of this solved it. :)

[Das Delfin]

Nice! Glad to hear it was an easy fix!

[IceWhite]

Nice! Glad to hear it was an easy fix!

This.

Sorry to hear about your other light :(

And this too.

[dsphil]

This.



And this too.

Thanks. Waiting for a replacement lens to come in. It baffled me how it can read the voltage and current but not enough to light up the bulb. This means that sometimes a bad connection will give false diagnose to a good sensor.