Headlight failure on Buick LeSabre

[RickNa]

In diagnosing a headlight failure, I've found that after removing the fuse and testing the voltage at the fuse socket, there is only 3VDC. The other working headlight fuse reads 12VDC. Further investigation show that the ground side of the fuse has no continuity to ground. If I put my voltmeter on the hot side of the bad headlight fuse and the ground side of the working fuse, I get 12VDC. So apparently the ground issue is in the fuse wiring inside the fuse box. I cannot remove the fuse box as I cannot get enough slack on the wire bundles going into it. I'm looking for a way to fix this by somehow getting a ground to the bad one. Everything I try results in a blown fuse since I'm sure I'm just creating a dead short. Novice electrical person here, just apparently know enough to be dangerous. ;-) Thanks!

 

[DPG]

I think the reason you are blowing fuses is that you are connecting a ground to one side of them. A fuse does not have a ground, it is wired in series with the load (ie the headlamp in this case).

The sequence is: Battery positive, fuse, headlamp, return to battery negative.

Obviously I've missed out any switches or relays there to keep things simple.

 

[RickNa]

I think the reason you are blowing fuses is that you are connecting a ground to one side of them. A fuse does not have a ground, it is wired in series with the load (ie the headlamp in this case).

The sequence is: Battery positive, fuse, headlamp, return to battery negative.

Obviously I've missed out any switches or relays there to keep things simple.

I see, thank you. I'm still at a loss on how to fix it. So if the working circuit has 12V when I remove the fuse and put the meter into the fuse holder, what would cause the other one to only show 3V. And if I check continuity to ground on the good one, it's fine but on the bad one it's open. So looking at the wiring diagram (which I attached here), the problem would be at G103 (on inner body panel)? So would running a ground somewhere after the headlight solve the problem? I can't locate the G103, I tried. Thanks again.

 

[brianmoooore]

If you are measuring 12 volts across a fuse, that fuse is blown. A good fuse will have no measurable voltage across it, whether it is passing current or not.
Check that you have two good fuses fitted and then check the voltage to ground at both pins of the non working headlamp.
If you have 12 volts at BOTH pins, then the ground wire from that light is faulty.

 

[RickNa]

If you are measuring 12 volts across a fuse, that fuse is blown. A good fuse will have no measurable voltage across it, whether it is passing current or not.
Check that you have two good fuses fitted and then check the voltage to ground at both pins of the non working headlamp.
If you have 12 volts at BOTH pins, then the ground wire from that light is faulty.

When I said I checked the voltages at the fuse, I removed the fuses first giving me the readings of 12 and 3 volts. And yes going from the fuse socket of the bad circuit's hot to the good circuit's ground gives me the 12V. I won't have the car until Saturday to try the fix but your diagnosis is the same others have given me locally. I'll probably have to isolate the ground wire going to the lamp, splice in a pigtail there and ground it to the frame. I was unable to locate where the ground is attaches. Thank you very much for your advice. I'll report back after Saturday. Have a good day.