Recently I noticed that my passenger side headlight was not coming on. High beam worked fine but no low beam. I bought a new set of bulbs and thought in short order I would replace both sides and the problem would be resolved. I installed the new bulb in the passenger side socket, turned on the lights and still no low beam on the passenger side. I pulled the bulb from the socket and a meter showed over 12v on both the high beam and low beam sides of the socket when either were switched on. Put the bulb back in but still no low beam. Pulled the bulb again and tested both sides of the socket with a test light. With the high beam switch on, the test light lit. With low beams on, no light on test light but still 12v on meter. I thought that there might be a problem with the socket so I replace it. No change. Went to the fuses checked them and even switched them. Fuses are good and the driver side still works fine with either high or low beams.

I don't get it. The meter shows 12v on the low beam side of the socket but won't light a test light and will not power the bulb. Any ideas? Thanks!

 

This is a good lesson for everyone who doesn't know. The amount of voltage drop through a resistance or bad connection is determined by the amount of current flowing through it. Your meter uses very very little current to run it, that is the reason it's so accurate. But that tiny bit of current, doesn't present any voltage drop through the bad spot or resistance. That is why you are getting 12v with the meter. The headlight bulb and the testlight draw a lot more current than the meter. So the voltage drop through your problem is higher, so the bulb doesn't work. If you could use the meter and have the bulb plugged in at the same time, you would see very little voltage on the meter.

But that doesn't solve your problem, Were is it? First rule, always leave the bulb plugged in to present a load on the circuit. I think the next thing I would do is turn the lowbeams on, with the bulb plugged in and check for power at the fuse. It should be fuse # 47 in the underdash fuse panel.

 

Do you mean pull the fuse and check where current would come into the fuse? Check with meter or test light? Thanks!

 

With bulb in socket I pulled the fuse. Showed over 12 volts on meter. Checked with test light and it lit.

 

Make sure to always keep a load on the circuit. Can you check for voltage at the fuse with the fuse plugged in? I know the older larger style fuses had a little spot on them where you could put the sharp point of a fuse. Not sure about the smaller type.

 

I'll check.

 

Okay, with the bulb in socket and switch on and with the fuse in place the meter showed voltage. You are right, there is a little spot on the fuse where I could test. Voltage was about .5v lower than what the battery itself showed but still plenty to light the bulb. The test light at the fuse did illuminate. The bulb still did not illuminate. I tried checking continuity between body ground and the fuse with the bulb out of the socket. There was continuity. Seems odd. A very low drawing short? Or is there some other place in that line where it could pick up continuity?

There seems to be meter detected voltage at the socket end that will not light the test light but on the fuse end there is meter detected voltage and the test light illuminates. Gremlins at work I think!

 

You have a poor connection from the fuse to the headlight socket. Could be a damaged wire. Could be corrosion on the back side of the fuse box. You replaced the socket so you should be good there. I am not familiar with the harness in this vehicle, but there could be another large plug-in that has a problem.

P.S. Some where along the way the wires change colors to the headlamps. So there might be another connector somewhere for them that might have a problem.

 

I'll see what I can find. Thanks for your help!

 

The wire that feeds the low beam on the side with the problem is green/yellow. I found it on a plug on the back of the fuse panel. I confirmed that this is the same wire by checking continuity. I clipped a wire to the positive side of one of the batteries to use to test. I touched both sides of the fuse with the fuse in place. The bulb did not light up. I put a needle through the wire on the back of the fuse panel and touched the needle and the bulb lit up. I think the breakdown is in the connection of the green/yellow wire to the plug or the plug to the fuse panel.

 

Excellent troubleshooting methods. Unless the wire is damaged, I would look at the back of the fuse box.

If you were in a hurry and pulling the fuse box looked like a job you did not want to take on right now, You could buy a fuse tap, put it around the fuse for the lowbeam on that side, and then plug a wire into the fuse tap and run it down to the wire you poked with the needle. You would have to strip the insulation back some to make the connection, but if it's inside out of the weather it should be ok. That would at least get you going for now and the circuit would still be protected by the fuse.