96 Legacy Headlight Problems

[captapd]

I’ve had an ongoing problem with the headlights on my 96 Legacy wagon that I would like some opinions on. In the summer of 2002 one of the OEM bulbs (the RH I think) started to dim and go bad. Since I have a long commute entirely in the dark in the wintertime. I decided to replace them with Polarg B1 Miracle White Halogen bulbs, which have the same voltage as the OEM bulbs. These worked fine for a few months until I noticed dimming happening again. Thinking the connector might be loose I pushed it back in and that cured the problem for a while. I had to do this several times. However after about a year both bulbs lost low beam and one lost high beam. I began to suspect some other kind of problem. On inspection both bulbs appeared to be fine (I did not electrically test them). I did replace blown fuse at one point, but that did not seem to affect the problem. After talking to the bulb distributor about melting and cracking on the Fujikura DC-L8PB-3FL connectors I purchased an aftermarket heavy duty wiring harness. This has not cured the problem either. I checked the Fujikura DC-L8PB-3FL connector with a meter and I’m getting 12 volts. A friend tested the Polarg B1 bulb that had gone completely bad and told me that the meter showed a bad bulb even through it appeared fine. I now have a Polarg B1 and OEM bulb in the headlights. They work O.K. on high beam, but don’t appear to be working full strength on low beam. I’m wondering if I have a short or some other electrical problem that is killing the bulbs. Any thoughts?

[theotherskip]

dim bulbs means that you are not getting full voltage (12V) across the bulb. in order to test this, you must check the voltage across the bulb with the lamp on. if you just probe the connector (not connected to the bulb), you will get 12V. you can try measuring the resistance between the 12V supply to the bulb and the battery positive terminal (should be very low - less than 1 ohm). be sure that the ignition is on and the headlights are on so the relay will be closed. then check the resistance between the negative connection to the bulb and the battery negative terminal (should also be very low). i would most likely suspect a headlight relay with dirty contacts or a bad ground. it probably isn't the bulbs...

[hklaine]

You mentioned upgrading to a heavy duty wiring harness. How is this harness wired and what does it include? Is it just new H4 sockets with heavy wire or does it utilize a relay?

 

I know that tracking down the problem and fixing it (then upgrading anyway) would be the ideal solution, but that can be time consuming and darn near impossible so if there isn't a short, and everything is fused for safety then I would recommend wiring the harness with a relay such that it uses the original headlight harness strictly as a signal for a relay and run power to the relay straight off the battery and then from the relay to the headlights. This way a voltage drop in the OEM headlight harness won't affect your light output (as long as the drop doesn't fall below critical voltage of the relay).

 

Wiring the lights this way will decrease voltage drop even in a system w/o problems and possibly increase light output.

 

[source: Hella KG Hueck AG, Germany]:

When operating voltage drops to 95 percent (12.825v), headlamp bulbs produce only 83 percent of their rated light output. When voltage drops to 90 percent (12.15v), bulb output is only 67 percent of what it should be. And when voltage drops to 85 percent (11.475v), bulb output is a paltry 53 percent of normal!

 

If your upgraded wiring harness included a relay and you have it wired this way (using OEM wiring for signal only) then I can't explain your symptoms. Short somewhere? Bad relay?

 

Hope this helps.

 

-Heikki

[Tiny Clark]

My 96 Legacy doesn't have daytime runnimg lights. but if your 96 does, amybe there is a problem with the control module.

 

As theotherskip said, check the voltage with the bulb connected.