MyE28.com

That's what I found last night.
This reading is from the harness where it plugs into the tail light assembly.
All other lights in this left assembly work as they should.

Where are you measuring voltage, between what two points? My first guess would be a bad or open ground somewhere.

I disconnected the plug from the taillight assembly.
I get 7 +/- from the ground and the positive that powers the tail light.
All other positive wires at that terminal when measured with that same common ground read 12 +/- volts.

I've also swapped out the check relay and get the same readings.

Maybe first check out fuse 10, then check out the light switch.

All the lights in all other assemblies on the car work as designed.

Fuse 10 checks out good on both sides with the light switch on.
The GY/YL wire going into the REAR LIGHTS CHECK RELAY only reads 7 +/- volts with the light switch on.

Looks like I have a fault somewhere along that GY/YL wire.
Short of pulling the entire harness, any suggestions? Common pinch points?

What do you get when you check it with it plugged in? I can't remember, but I think you can stick the probes in the back of the connector. I bet it goes to zero. Next check fuses, looks like 9 and 10. Check for voltage on both sides of the fuse.

Mike W. wrote:What do you get when you check it with it plugged in? I can't remember, but I think you can stick the probes in the back of the connector. I bet it goes to zero. Next check fuses, looks like 9 and 10. Check for voltage on both sides of the fuse.

Just did and edited the above post, and it does go to zero plugged in.

It goes thru the check control relay, I've heard of problems with them, though I've never seen it. Check for voltage both in and out of course. Looks like gray yellow going in and gray blue coming out.

Mike W. wrote:It goes thru the check control relay, I've heard of problems with them, though I've never seen it. Check for voltage both in and out of course. Looks like gray yellow going in and gray blue coming out.

Swapped in a known good one and no change.

1st 5er wrote:All the lights in all other assemblies on the car work as designed.

Fuse 10 checks out good on both sides with the light switch on.
The GY/YL wire going into the REAR LIGHTS CHECK RELAY only reads 7 +/- volts with the light switch on.

Looks like I have a fault somewhere along that GY/YL wire.
Short of pulling the entire harness, any suggestions? Common pinch points?

Temp fix would be to use the right side as power.

demetk wrote: Temp fix would be to use the right side as power.

... or drive during daylight hours only.

It looks like you're getting resistance on the wire somewhere along it's path. Which is a pain in the butt to pinpoint. If the fuses/ACC relay/bulbs etc check out, I'd trace the wire.

Open the insulation a couple inches, from the tail light forward. Possibly a frayed or broken conductor inside the insulation, they can break from vibration or rough handling. If your trunk is wet maybe you have some corrosion on the crimp. Don'tcha love tracing wiring problems?

I hate to ask the obvious, but......are you sure it's the supply and not the ground? Use a known good ground. If you don't have one, run a wire to the battery negative from the meter,16 gauge.

Coldswede wrote: Don'tcha love tracing wiring problems?

NO!!!

bavarianautowrks wrote:It looks like you're getting resistance on the wire somewhere along it's path. Which is a pain in the butt to pinpoint. If the fuses/ACC relay/bulbs etc check out, I'd trace the wire.

Everything else in the circuit checks out, so it's trace time.

waynet1 wrote:I hate to ask the obvious, but......are you sure it's the supply and not the ground? Use a known good ground. If you don't have one, run a wire to the battery negative from the meter,16 gauge.

I don't see how it can be the ground if all the other lights in that fixture work.
I'm pretty sure it's one ground for the entire fixture.
Hopefully I'll have time tomorrow before the rains predicted for the next several days start to get to the bottom of it.
First thing I'll do is recheck everything.

1st 5er wrote:

waynet1 wrote:I hate to ask the obvious, but......are you sure it's the supply and not the ground? Use a known good ground. If you don't have one, run a wire to the battery negative from the meter,16 gauge.

I don't see how it can be the ground if all the other lights in that fixture work.
I'm pretty sure it's one ground for the entire fixture.
Hopefully I'll have time tomorrow before the rains predicted for the next several days start to get to the bottom of it.
First thing I'll do is recheck everything.

That's why I asked what points you were measuring between. I don't think that's the problem now, but the ground on E28 taillights is two pieces of galvanized steel just kind of folded against each other. Dave C had terrible brake light problems I didn't figure out until he replaced his lights that were due to the two halves around the taillight not having good continuity.

Mike W. wrote:

1st 5er wrote:

waynet1 wrote:I hate to ask the obvious, but......are you sure it's the supply and not the ground? Use a known good ground. If you don't have one, run a wire to the battery negative from the meter,16 gauge.

I don't see how it can be the ground if all the other lights in that fixture work.
I'm pretty sure it's one ground for the entire fixture.
Hopefully I'll have time tomorrow before the rains predicted for the next several days start to get to the bottom of it.
First thing I'll do is recheck everything.

That's why I asked what points you were measuring between. I don't think that's the problem now, but the ground on E28 taillights is two pieces of galvanized steel just kind of folded against each other. Dave C had terrible brake light problems I didn't figure out until he replaced his lights that were due to the two halves around the taillight not having good continuity.

Are you saying I need to check the integrity of the metal that surrounds the taillight and acts as the ground for each light?

Here are my measuring points:
1 - at the light assembly;
From the plug, with it unplugged the reading between the GY/BU and BR produced 7 +/- volts.
With it plugged in voltage reads 0.
2 - at the REAR LIGHTS CHECK RELAY;
I measured between the GY/BU and the BR, 7 +/-.
I also measured between the GY/YL and the BR with the same results.

Thanks so far.
I'm sure it's simple, and I'm simpler, thus stumped.

I'll swap in another complete taillight assembly tomorrow and report back.

Swapped in another taillight assembly, same symptoms.

If I run direct 12v to the taillight assembly either at the plug-in or on the individual exposed metal circuits all the lights work.

Time to start tracing, I think, or at least that's what I'm about to start.

I must apologize Sherman for not reading your posting more carefully. You did in fact say that you were using the same B- when checking the other voltages, and they were fine.
After rereading all this, I would attempt to locate S212 pin#1. Might be some corrosion or bad connection there.


Sorry I'm not there to assist, I love a good wiring mystery.

It's for sure kicking my butt.
I'll give S212 a look see.

Thanks.

Good news / bad news;
the light is now working, but didn't find S212.

I removed the knee panel but didn't find any GY/YL wires so out came the cluster.
Still no GY/YL wires in plain sight so after rustling around a bit I decided to try the lights again, and BAM, it's on.


Oh well, I tightened up my Cruise Control stalk and I'll install my Pedal Bracket Support
and periodically check the lights as things go back together.

Hmmmm?

Sound like all good news to me.

You obviously were in the right area and jiggled the bad spot.
That's certainly where I would start looking for S212 as well. The diagram is sure vague as to the location.

waynet1 wrote:... locate S212 pin#1.

I understand and see in the schematic S212, but what/where is "pin#1" referencing?

1st 5er wrote:

waynet1 wrote:... locate S212 pin#1.

I understand and see in the schematic S212, but what/where is "pin#1" referencing?

I'm assuming that S212 is a connector in the harness. The GY/YL wire would be on pin#1 of said connector. Not that you really give a shit what pin number it is.

waynet1 wrote:

1st 5er wrote:

waynet1 wrote:... locate S212 pin#1.

I understand and see in the schematic S212, but what/where is "pin#1" referencing?

I'm assuming that S212 is a connector in the harness. The GY/YL wire would be on pin#1 of said connector. Not that you really give a shit what pin number it is.

I only saw one GY/YL wire under the dash and it went into a connector up against the firewall,
and it was a in a second row upper left middle position.
Guessing I should check that that connector is clean and secure.
Because of schematic 6314-1 I was looking for a 3 wire splice.

Where, which schematic, did the "pin#1" info come from?

Found my problem.
Got out there and turned on the lights and started giggling wires.
It faulted the Check Control Panel light and here's what I found.
The wire connector in the above referenced plug was not securely pushed in.
I pulled the plug, pushed in the wire connector, replugged it back in, BAM!!! it stayed in and system didn't fault.

guys.

Outstanding.

I was just in the process of checking the diagrams I was looking at were the same ones you were.

Happy nigh-time driving once again!