amarucci89

Hi,

I own a 2004 Mustang V6 40th Anniversary model and recently noticed that my passenger side headlight is much dimmer than the driver's while in normal mode. As I checked the light, I noticed that the clip connecting the harness to the bulb was broken. But after checking, I realized that was not the problem so I changed both bulbs with new factory ones to see if that would fix it with no luck. What can be the cause of this?? All other lights/electronics function normally with no surges.

Thanks,

Alex

Daehawk

Ballast?

amarucci89

On my stock headlights? Isn't that more common with HID lights?

Daehawk

Yes sorry..so used to HID questions.

I'd guess it's a ground issue. Maybe loose but best guess is the ground on that side.

amarucci89

No problem, I checked the 2 grounds that are on top of the frame, cleaned them and made sure there was a good connection... are there more grounding points I should check? If so, where are they located because I cannot find any diagrams/photos of the headlight grounds online...

Thanks!

Daehawk

I've looked also and the one diagram I found was all in color and stuff but was so small i couldn't read it. Sigh. I do not know how many there are or where but the dim output in only one side and even wit ha new light definitely is a ground in my opinion. maybe someone on here can chime in folks?

LilRoush

Check the attachment point again at the back of the headlight housing. Those black plastic clips tend to heat up and warp over time...it allows the ground to come loose at random. Even if the wire is tight in the back, it might have lost full contact inside the clip/harness. The pigtails can be picked up at most local parts stores for about $5 each.

amarucci89

OK, well this is what I did.... a little piece of the harness clip was broken off so in order to keep the harness attached to the housing securely, I took a few small rubber bands and tied them around to keep it from comming loose (I know, its only a temporary solution) but even when I hold the two parts tightly by hand, the headlight does not seem to get any brighter. I'll have to double check those plastic housing clips you mentioned and report back as soon as I have time..

LilRoush

Try pushing the wires in and out of the harness ends a bit, see if that helps.

petrock

Dim output of a light is due to resistance in the circuit. While a bad ground is a common source of resistance in a circuit, it is not the only one. The resistance can just as easily be on the power side of the circuit or the connector itself. If the connector looks good and the pins inside it look good and wiggling the connector doesn't fix the problem, then the problem is in the wires. Simplest way to find the problem in the wires is via a voltage drop test with a multi-meter/volt-meter. If memory serves, there should only be three wires going into the stock light socket. One for power to high beams, one for power to low beams and one for ground. First step is to figure out which wire is which (if you have the circuit diagram, skip to the tests below, otherwise read on). Unplug the connector and turn on the low beams. The wire that has 12 volts is the low beam power wire. Then turn on the high beams. The wire with 12 volts is the high beam power wire, which makes the remaining wire the ground wire. Now to start the test. Plug the connector back in and switch to low beams.

- Take a safety pin or thin needle and back probe the low beam power wire in the connector
- Touch the negative lead of the multimeter to the positive battery post and the positive lead to safety pin. You should get no more then 0.5 volts. Any more then that and you have resistance somewhere between the pin and the positive battery post.
- Take the safety pin and back probe the ground wire.
- Touch the negative lead of the multimeter to the negative battery post and the positive lead to the safety pin. You should get no more then 0.5 volts. Any more then that and you have resistance somewhere between the pin and the negative battery post.

Resistance can be any number of things, including but not limited to loose and/or corroded connections or damaged and/or corroded wires. To find the point of resistance walk up the wire towards the battery with the positive lead until you get a reading you expect. The resistance is between the first point that produces a reading you expect and the last point you got a bad reading.

Note: I said to touch the battery post with the multimeter lead, not the battery terminal. This is because the resistance can easily be in the battery terminal (loose/corroded connection).
Good luck...