Subaru Outback Tail Light Relay

[TedZ]

I love this forum and have searched to tears on it for the problem with the clearance lights that don't work on a 2002 Outback.

 

Looking for the tail light relay. It is not in the main fuse box under the hood and not in the fuses under the dash (behind the pull out junk "ashtray") Perhaps there is no relay, i don't know.

 

I am a good "meter man" being an EE and i have checked every connector remotely associated with the clearance lights and all measure appropriately either to ground - where they should - or through the light filament where appropriate. Yet when turned on fuse 5 under the dash blows instantly.

 

When i powered the clearance light directly (i have the alligator clips with small spikes on them...love them) i thought the right rear was showing signs of being dimmer but the 16 ga. wires to the lights were both getting warm equally. (I was connected to a low ampacity source...suppose i could try it from the battery).

 

My questions are: Where is the relay, if any. Has anyone had a light fixture go bad and cause this? Could a bad bulb do this??!! Does the headlamp/tail light switch go bad ever??

 

Thanks

[OB99W]

Obviously, there's a short to ground of relatively low resistance. There's a "trick" I sometimes use when troubleshooting this kind of problem. Take one of the blown fuses, and wire a lamp of reasonable current draw (a clearance, stop, or turn-signal type, for example) across the fuse; use long enough leads so that you can place the lamp where you can see it anywhere around the car. Plug the fuse/lamp back into the holder, and turn on the lights. If a low-resistance short to ground exists, the lamp will light at very near full brilliance. You can now go around and try moving suspect wiring, remove suspect bulbs, etc., while watching the test lamp (out of the corner of your eye?) at the same time. If the test lamp gets dimmer (due to voltage division, if we need to get technical ), you've found the problem.

[TedZ]

That is a great idea. No light, no short to ground.

 

I would still love to know if there is a tail light relay anywhere as the short may show when the coil is energized...fried coil, or the light may not light unless there is an energized coil somewhere revealing the short to ground and then lighting the test lamp.

 

Thanks.

 

Ted

[OB99W]

[...] No light, no short to ground. [...]

Not quite. Any time a ground short is there and power is applied, the lamp will be at or near full brilliance. However, when the short is removed, the test lamp and the normal load will then be in series; there will still be a path to ground through whatever is that load. Therefore, the test lamp's light output will be reduced, to whatever degree the voltage division between the test lamp and the normal lamp circuit determines. The test lamp would only go out completely if both the short were eliminated and the normal load were removed (in other words, no path to ground existed at all).

 

The reason I've suggested a test lamp rather than just a meter is that the eye is sensitive enough to readily detect changes in brightness, but you have to pay closer attention to meter readings. Furthermore, lamps have non-linear resistance with respect to applied voltage, and that complicates interpreting the readings. If you find it useful, you could put a voltmeter in parallel with the test lamp; when the short is removed, both the lamp brilliance and the meter reading should drop.

 

I don't have a wiring diagram for the '02, just the '01. Fuse #5 in the fuse/relay box is shown as 10 amp -- is that the value of the one you're referring to?

 

There is a tail/illumination relay, at least on the '01. However, it appears to precede the parking switch in the circuit, so isn't a likely point of a short.

 

There are a few ways to approach this. One is to start pulling connectors, and see if you can isolate the short. Another, if you suspect a shorted lamp, is to pull all of the ones on the circuit, one at a time; that includes the front clearance lamps, the rear finisher and tail lamps, and the license plate lamps. There's also the trailer connector to consider.

[OB99W]

I though this problem sounded familiar, so I searched a little, and found this: http://www.ultimatesubaru.org/forum/showthread.php?t=81603 .

 

Do we not think this is possibly related?

[TedZ]

Hi and thanks. You are right, forgot about the original load providing a path to ground also.

 

Fuse number 5 is a 10 amp fuse in the '02 Outback and that is the one that blows.

 

I thought the deer crash and this problem were related right from the beginning but i came to doubt that after ringing out every connector on the car and finding no differences in right or left front connections anywhere. I have observed some issues in the right rear and that is where i am going to "play" with the test lamp etc.

 

Thanks again for taking the time to answer my post and for the education on test lamps:) .

 

Ted

[porcupine73]

A couple things that came to mind....

 

I saw some endwrench article not sure if this is useful http://endwrench.com/images/pdfs/ErraticInsideNov07EW.pdf

 

Not sure about all soobs, but on my '94 there is some relay box or something in the rear right taillight housing area:

[TedZ]

Just to close the loop on this thread, the tail lights are fixed. There was a short in the wire going from the under dash fuse panel to the Security Control Module. No one had ever run into this, so i want to post it here just in case there is another unfortunate.

 

A dealer in Norwalk CT found it after hours of looking. They kindly only charged my for three hours labor because they felt they should have found it sooner!

 

I didn't think there could be a wiring problem i couldn't find given enough time. So much for that thought. I knew there was a wire going to the SCM from looking at the wiring diagram but i never checked it.

 

Thanks to all who responded with great info. I learned a lot for the next time!

 

Ted