jeff spahn

I have stated before on Rennlist that I am no electrical genius (like Alan).

I have a tail light out that I cannot figure out. I don't even know how to begin.

Mechanical issue, no problem. Electrical, might as well be an automatic transmission with magical blue smoke mixed in. Ask me to figure out software, no problem. Electrical troubleshooting. I am a dufus.

Now, if you give me direct information, I can follow that to a tee. Hell, I learned to fly a plane at 45, I can follow directions fine. I pulled the engine, replaced a piston and did a tb/wp/porkensioner job no problem on my 928 but that is all mechanical stuff.

So (electrical geniuses out in Rennlist land), how to I figure out why my taillight is out.

Yes, I checked the bulb. It works perfectly on the other side. I wiggled the connection. No change.

How and where do I begin. Wiring diagrams might as well be spaghetti to me. must be because I am left handed.

joejoe

This sounds similar to my problem with passenger brake. Take a look at it and follow wallys' suggestion. On mine there was a short in the hatch wiring causing both 3rd and passenger brake light not to work.

FredR

Jeff,

Presumably you have checked the obvious to ensure there is [or is not] a voltage arriving at the bulb connector? Even the dumbest electricians can do that. I seem to remember that there is a connector back to the harness- check there is voltage there.

Thereafter just a question of working backwards until you find signs of life/discontinuity. Quite possible you have a "dry joint" in the bulb holder, that or a joint has failed completely.

Good luck- if you can do all the things you have listed you can certainly do this.

On the wiring diagrams it helps greatly if you take a photocopy of the applicable sheet[s] and use a highlighter pen to track the circuit. there is nothing complicated in that part of the wiring harness as it works its way back to the relay/fuse board.

Regards

Fred

MFranke

Sometimes this is due to socket degradation. Check the socket for corrosion. If corroded replace with the Nissan Quest socket - there is a thread somewhere on these boards describing this inexpensive fix.

Then address the root cause. If is was corroded then need to find water source. Some have experienced issues with cracks or holes in the plastic assembly above the bulb that allow water in. A thin strip if black weatherstrip across the top of the tail light assembly can keep the water out.

Alan

First off - describe what you mean exactly.

Tail light out is very generic - too generic...

This is one marker light only? or all marker lights?

Does it affect brake lights?, reversing lights? turn signals?

Is the lamp totally out? or dim?

When it is supposed to be on does is affect any other features in any way that isn't normal?

Start with a good description of the problem, when did it start doing this? - was this preceded by some work on the

Did you change bulbs?, go to LEDs etc recently?

You did check the fuse already right?

Alan

MainePorsche

Jeff,
Fred, Mark, and Alan are on point. Do you notice water build up in the tail light unit ? Even condensation ? I did on my passenger side to ? I couldn't find the ingress point however. What I did do was make an egress. I drilled two small holes on inferior surface. Allowed for gravity driven egress of water, and also acted as kind of a vent to this sealed chamber.

As to not being able to decipher a Wiring Diagram, see this link https://rennlist.com/forums/928-foru...am-phobia.html
Alan's work here should be required reading in the Rennlist 928 '101' course.
Now Jeff, you will have no more excuses re electrics.

newworld

87s4 aut. running light out left rear and side marker.....it is intermittent. sometimes flickers on and then goes off only one side. all brake reverse for left work. headlights all work.

i must have tore apart the left rear tailight 30-40 times. i even replaced the whole socket with napa replacement. i still have a problem.

left side rear running lights and side lights do not work most of the time when headlights are on.

i dont know what else to look at. all new bulbs, it will come on occasionally.

then go off and i get a tailight warning on dash.

jeff spahn

Here's the part I am talking about. Sorry I wasn't clearer.
This only happens when the headlights are on. Brake light functions normally with lights on or off. Only tail light portion of this bulb doesn't function when I turn on the lights.

jeff spahn

I did order Alan's book (I think it was Alan's). I believe I only got a short version of the book.

I re sealed my tail lights about three years ago after getting water in them and blowing (like shattering) brake light bulbs. They were melted above the brake light part. I repaired all of that.

I have drilled drain holes in the bumper under the tail light to prevent water from accumulating. I believe Porsche had this as a Service Bulletin. I have also used a gasket lubricant on the rubber portion of the bulb carrier as indicated in a service bulletin. Since doing all of this I have had no water or condensation in my tail lights for over three years.

MainePorsche

Doesn't sound like a ground issue if your ipsilateral sidemarker functions. You've said the double filament bulb functions normally when you put it on the other side. Then must be a bulb socket issue of that tailight or the wiring to it. I'm not at a WD so I can't say what color to look for. Sounds like the hunt is on.

newworld

alan--
where are the ground points for the side markers and running tailight left side when the headlight is on?

i looked inside engine bay left side, and could see one ground near ignition amplifier in front.

87s4 aut.

MainePorsche

The ground points for rear lights are on the front wall of the spare tire well. You'll see them.

Alan

So its not a fuse (there aren't separate ones).

Since its only one segment - Seems its either the bulb, the socket or the local wiring in the cluster.

First did you try changing the bulb for a fresh one? - fresh ones seat to the socket better

Take out the bulb and look in the socket - does it all look clean in there?

change out the bulb for a new correct 21W/5W make sure you install in the correct orientation (see the offset bayonet tabs).

Report back?

Alan

jeff spahn

I put response above.

MainePorsche

Again, socket or local wiring fault.