pvoth

where is it on my 82....more info... my ! light comes on and says my tail light are mucked up.....they work but I changed them anyway hopeing maybe that would fix it.... it still comes on....damn
anyone have an idea what to look for!!!!! thanks everyone
p

Bill 86.5 928s

Hey Paul...On my 84 I would get a warning of the tail lamp and it was a side marker light that was generating the fault. I still gives the warning to this day as I haven't fixed the problem yet. I just tap the light and the warning goes away and the light comes on. Someday I'll look at it....yeah right, it's been two years now. Good-luck ...Cheers Bill

Steve J.

Maybe this is my problem with the '87. I have a tail light fault light but have replaced the bulbs (in pairs). Can someone confirm that the side markers can trigger the tail light out indicator? I do have a side marker out.

John Struthers

Confirmed!

T_MaX

Yep all exterior lights, except headlights can trigger the Lamp Control Unit (LCU).

At one time I had found a Service note on the early models needing an extra ground to be added to the LCU.

I'll see if I can find it again.

John Struthers

MAX,
PUHLEEESE DO!

I feel like that good Captain strapped to Moby Dick.
I've got the rear facia off, disassembled the tail lights all good back there including license plate light wiring. after the TT pinch bolt check -exhaust down, heatshields off, inspection holes open- I'll drop her down and pull the interior panels-interior quarters- and work forward - ....

Dennis Wilson

The system compares resistance on both sides and triggers the warning light if there is a variance. Listers have reported the warning light has came on when two different brands of bulbs were used. Also a corroded receptacle, fuse or ground on one side may be enough to trigger the warning light even though the tail light works.

Dennis

SteveG

Maybe this post is pointless b/c I can't remember the circumstances EXACTLY, but the fogs are on alone or w/headlights or both and I get tailight warning that stays on until the fogs are shut off. All lights are functional. The only aftermarket item this is a radar wired into the cig. I guess I should start looking at the fogs, but it hasn't been an issue.

John Struthers

Dennis,
Danke Schone.
But, If I have the car all apart like this and still can't find the problem I'm going to blame it on the LCU.
I've replaced that puppy once and won't do it again. If my trace to the front both sides doesn't turn something up I'm going to bypass the mrker/running lights for both rear circuits by cutting and capping the feed before the LCU and may do the same for the brakepad warn if the new sensors don't eliminate the problem.
I have a good feed & ground to both rear circuts -sockets are shining, all soldered connections are factory fresh looking, even removed about an inch of insulation from all rear wire connections looking for hidden corrosion then recovered and taped, PIA-
Bulbs are all new and matched from same package and manufacturer.
No crimps or pinch points, so far, I'm working my way forward.
If and when I cut into the power before the LCU I will be a nice guy and solder connectors to any loose wires and tape/bundle them off in case a future owner is a purist and wants to hook back up to a new LCU.
If the LCU is the problem I'll be damned if I buy another one as to me the thing is non-essential and a Waste of space. Since I don't have a TB tension Warn, or ABS on my 82' all I care about is the following gauges:
Oil Pressure, Alt, Water Temp , Fuel.
I can tell when its time to check the brakes, and fluids/lights/tires are regular inspection items.
Hand me the diagonal cutters, please.

SilverSFR

SteveG,

Same exact thing happens to me. When I turn the head lights on, I get the tail lamp warning to come on. This sounds like a group winter project to me.

STEP 1: Everyone, clean all the sockets to all the bulbs (including the
side markers) in the rear tail section.

Who has step two?

SilverSFR

T_MaX

I'm still looking through the service information 1979-1994, but I remember reading a small one liner that states the ground for the LCU was insufficient and would cause this problem.

The fix is to add a ground to the LCU. It would be worth a try before cutting your shark up.

Back to my reading

John Struthers

Silver,
From my growing wealth of hard-learned info.
Does the taillamp warn appear with just the runnining light/marker lights on as well or only when you turn on the headlights?
Try with just the fogs and running/markers while you are at it.
I've been wrestling with mine since early 2002.
Steve Cattaneo sent me some electrical wire run info and I confirmed it with a physical trace.
Keep in mind I sometimes call the parking lights>running lights, O.K.?
Also, Keep in mind that although the front and rear lights are on 'different circuits' the entire left side marker/parking light 'system is fused thru the same fuse and the entire right side marker/parking light system is fused thru its own seperate fuse.
As Follows:
1. Left front side markers and left front parking lights are on the same circuit. Feed/activated thru the light switch. Fused thru fuse #28 at 8amps.
Wire connection is M5 on the fuse/relay board. Grey/brown wire which runs thru a 4 pin plug in the fwd left wheel well -remove splash shield. The colors run from the grey/brown wires at the plug to 2 blue wires.
2. Right frontside markers and right front marker lights are on the same circuit. Feed/activated thru the light switch. Fused thru fuse #29 at 8 amps.
Wire connection is M6 on the fuse relay board. Gray/red wire which runs thru a 4 pin plug in the right front wheel well .
The color are grey/red feed at the plug to 2 blue wires.
At the LCU I get a little fuzzy:
The LCU because of it's function as a olid state warn/alert to the pod and central warn sysytem has multiple feeds at 12 seperate pins, for a solid state device its pretty darn big.
Pin 6 and pin 7 are grey/brown junctions but I'm not sure which one is for front left or rear left, same for pin 4 and pin 5 which are grey/red, not sure which is front and which is rear.
3.The Left rear marker and running lights are on the same circuit BUT fed from the LCU. It is fused thru fuse #28 at 8 amps ( the same fuse as the front left ) . The left rear wiring is Grey/Black that runs to a 4 pin connector in the spare tire well. At the pins the wires are straight gray and go to the bulbs.
4.The Right rear marker and running lights are on their own circuit but fed from the LCU. It id fused thru fuse #29 at 8 amps ( the same fuse as the front right) . The right rear wiring is Grey/Red that run to a 4 pin connector
(sometimes located in the spare tire well. sometimes located behind the tool kit cover, sometimes located behind the right rear interior 1/4 panel cover seen em all and they all look factory...?)The color out of the connector is just like the left side -, GRAY to the bulbs.
Hey on the up side you only have 10 more pins on the LCU to work thru.

T_MaX

I'm still looking for my ground wire referance!

But I thought I would share what I see in the wire digrams.

_______________________________________________

As per the wire diagrams for a 1982 928.

Items that are run though the Lamp Control Unit (LCU)

Side marker left.
Rear light left.
Brake light left.

Side marker right.
Rear light right.
Brake light right

------------------------------------------------------------------------------

Items that are not run though the Lamp Control Unit (LCU)

Turn signals front left.
Turn signals rear left.
Side marker left
Parking light left
Back-up light left.
Fog light left

Turn signal, front right.
Turn signal, rear right.
Side marker right
Parking light right.
Back-up light right.
Fog light right.

License plate lights
Headlights

PorKen

John Struthers,

If you're going to remove the brain, don't hack the harness, do it the factory way...

There was a factory jumper to bypass the rear light brain (LCU); I made one:

This connector is found on 80's Mercedes (easily found in the U-Pull junkyards), a 12 pin I got from under the dash, on the passenger side. The pins are soldered so it is easy to rewire these. (Made the lights a bit brighter too?) Note that different years had different brains, so check your wiring diagrams! (This is for 81)

H2

I had the problem of the tail light warning light on...and all lights worked....so I replaced with the same brand and it went away. Maybe that fixed it or me jiggling something. I dont' know. But for year and half it's been fine.

Harvey
'85S