notaguru

On this '83 US-spec with AT, the red Achtung! illuminates once in a while.

Guru Greg thinks it's the light sensing circuit, and that the car is sensitive to GERMAN bulbs. I tested the wiring, replaced all bulbs with Hochdeutsch, and refreshed connections, but the problem persists - at least once daily now I'll get the alert. An observer confirms that all exterior lights work properly whether the alert is ON or OFF.

Is there a way to disable that sensing circuit?

THANKS!!

Alan

Why not replace the dash bulbs that must be burned out - so you know what the actual cause was before disabling something that may not really be the cause and that performs a useful function when working correctly.

If you have the correct bulbs in place - it may well not be that.

Alan

notaguru

Thanks.

The dash bulbs all seem to work, as do the exterior (rear, front, side) lights. There is a possibility that a circuit irregularity (cold solder joint, oxidized connector, wrong bulb, etc.) has changed sensed resistance, if that's what is sensed, to trigger that annoying OCCASIONAL alert. I used a 10ohm power resistor to load each accessible point in the circuit, and measured close enough to an amp everywhere.

The only light that is inoperative is the driver side door courtesy light - bad bulb. But with the door closed, that should not be involved.

I would be happy to simply disable that alert function.

Alan

Does it tell you it's a brake or tail lamp warning? You should get a specific warning if all warning bulbs are good

Alan

notaguru

"Tail lamp" - and only when the exterior lights are ON. However, the red alert appears (1-2 times a day) when the exterior lights are OFF.

It's probably a big bridge that senses assymetrical current flow between bulb pairs, though I don't know how or if it sees turn signals. It should be trivial to shunt or open that sensing circuit to kill the alert, but I do not know where to do it.

Alan

If you get an alert while the lights are off it isn't from the bulb monitor. Obviously you have some other issue with the lights when they are actually on. The 2 rear/sidemarkers are also checked (in conjunction with the tail lights) - did you replace those bulbs also? If not do that next - and clean up all the bulb holders. Any resistance there affects the readings.

On later cars the test method is they add a small series resistance in the supply to each side and compare the voltage dropped across them side to side - any difference above a threshold causes the warning - testing can only happen when the bulbs are activated. Not sure if this holds directly on an '83 - very early cars had a system using reed relays (but still a similar concept). The later models use Op Amp type comparators.

Alan

notaguru

The Tail Lamp light illuminates only when the exterior lights are ON. The general alert occurs with exterior lights ON or OFF. It typically appears when dropping from highway speed to neighborhood speed, whether or not the brake pedal is touched.

I just pulled the pass side rear lens. Forgot to mention earlier that the brake light assembly evidently got hot and melted some things. It's been put together with high-temp reflective tape, but I'm uncertain regarding the connections behind the socket.

Alan

Warnings with the tail lamps off are not the bulb monitor - check all the other warning bulbs during bulbs check - it is likely (one of) what ever does not illuminate then that should.

Bulbs melting the light assembles are either bulbs of too high a wattage installed OR poor connections at the bulb holder.

Alan

LeLutinBanni

Worked perfectly on my 87 S4

The connector is located at the right of the fuse panel.

notaguru

Good information - thank you!

Hopefully that connector exists in my '83 US-spec. I'll check tonight - and if it does I will try to DISABLE light sensing by disconnecting pins 7 and 10.

dr bob

Philosophical:

Fix the damn thing. Warning and alert systems are there for a reason. This one is sensitive to poor connections, corroded wiring, damaged sockets, mismatched bulbs. Solve those things so the lights work correctly, and the warnings will go away.

Disclaimer: I work too much doing event reconstruction following "events" in power plants. Too many are caused by folks who are smarter than the systems, who firmly believe that the first three warnings weren't really valid. Maybe tail lights aren't a critical system. I believe they can be in the dark.

Lizard928

1983 used a different bulb lamp controller which is bolted directly above the fusepanel.
I do agree with Bob though, it is better to fix, unless you're running LED bulbs.

notaguru

Of course it's better to fix, but that ideal solution has eluded me, Greg Brown, his mech, and a local auto electrics shop. We all tried, but that #$%!! Achtung! light still comes on at odd moments.

I hoped that someone here had encountered the same symptom, and found a solution.
SYMPTOM: warning light comes on 2-3 times a day, when decelerating (not braking). It's resettable in the ordinary way, and does not come back on.
SOLUTIONS TRIED: installed standardized bulbs, refreshed grounds, checked visible wiring, cleaned connectors (did not get behind the rear bumper cover), applied Cramolin.

I'm reluctantly willing to disable that part of the alert system.

docmirror

This thread is one of the types that kinda **** me off. Not because the OP wants to do something that we consider to be outside the accepted bounds of 928-ism, but because several of the wisest electrical guys in the group refuse to ANSWER THE DAMN QUESTION.

I don't have the answer, and I'm not in a place I can look it up, but it's pretty sad that some want to play 'I know the answer and youuuuuu don't!'.

Snark Shark

The '84-86 unit has a pretty hefty double induction coil on the circuit board that puts a lot of strain on the solder and creates cracks and intermittent problems. Reflowing the solder fixed mine. I bet the 83 has something very similar.