Electrical Tom Foolery

[Mr. E28]

My 94 530 is being weird. Just to start things off, on occasion, my tach would act funny (register much higher rpms than actual) upon turning on the lowbeams. This has happened since I bought it from the PO early last year. A couple of weeks ago, my headlights (HID) started working intermittently. Research led me to the LKM as being faulty. I ordered a reman (older lkm-l) to get me back on the road quickly until I could attempt messing with the original. I received the reman module, installed it, everything worked perfectly for a night of driving..great! A couple of evenings later (no night driving up until this point), all of the same issues returned. My headlamps didn't turn on initially, came on and went out, came back, then just the driver side went out, came back, etc. Then one of my fogs went out, yada yada yada.

Now things get weird. Sometimes while the headlamps aren't working, if I turn my blower on to a designated speed (sometimes 1 sometimes 4), they pop on immediately. I was able to repeat this occurrence 5 times in a row at one point. Sometimes the blower turns off when the lights do. My blower also works intermittently at certain speeds (I'm about to replace the resistor). Sometimes when both of them are not working at the same time, and the blower randomly switches on at whatever speed, the lights immediately return also. In any case, the headlights and the blower seem to be effected by each other for some reason. Do they share power somewhere? My lowbeam error stays on now as well. It never displayed until the issues started with the OE LKM, and stayed on even with the older reman. Throughout these recent events, the tach issue hasn't happened again. Could this still be an LKM issue?

[demetk]

Very strange happenings. It might be a good time to break out the multi-meter. Have you verified where the HIDs are getting power from?

[David325e]

Fusible link?

[jehu]

Do you have any water-where-it-oughtn't-be issues?

[Mr. E28]

It might be a good time to break out the multi-meter. Have you verified where the HIDs are getting power from?

The HID kit is installed as plug & play (not tapping power from anywhere else). The multi-meter will certainly be coming out when I get some time.

Fusible link?

I would not have thought of that. Everything else is working as normal (windows, locks, radio, etc.). Worth an inspection though.

Do you have any water-where-it-oughtn't-be issues?

Not that I'm aware of.

[David325e]

I forget what is powered by which. There's that 50amp leading off of one of the battery cable to contend with too. I've forgotten most of the little I did know, just thinking of temp. sensitive ideas. We're certainly having degree swings around here hahaha.

[PorscheH6]

The HID ballasts are causing your tach issue. Well documented on the forums

[Binjammin]

The HID ballasts are causing your tach issue. Well documented on the forums

And your cutting out issue is likely the relay on your LKM for the headlights.

[ross1]

Agreed about the LKM. re-man or not, the symptoms are classic. I'd like to know what goes into "remanufacturing" these. The relays go south on them causing the headlight issues. I also think they don't like different headlights.
I suspect the blower trouble is unrelated although VERY coincidental. Perhaps a vibration is causing the LKM relays to open or close, maybe a momentary power surge who knows but I can think of no commonality with the lighting. An intermittent fusible link wouldn't cause one headlight or only a portion of something to go off, rule that one out.
If you blower runs quietly a new resistor ought to fix that.
The LKM is high and dry so I wouldn't think water to be an issue, but who knows these cars are getting quite old. A new weird cause for something seems to pop up around here every week.

[jehu]

I have water in my carpet driver's side from holes in the underside... now I gather most people wouldn't even at that point care anymore and would have literally junked the car but that aside I recently smelled some ghastly burning smell after driving a while and had it towed home. It has sat for a week or so now and I drove it for a bit this weekend and found now the dome lights are not functioning, fuse was good, bulbs appear ok.

There had been intermittent "DOOR OPEN" messages while driving for some time with this moisture which abates when some drying takes place so I assumed some wires running from the driver's door striker microswitch were shorting from water assuming they run under the carpet from the B pillar. I have also had a door lock actuator individually cease operation a few times clearing up after drying.

I expect to get the carpet out when possible and examine the wiring which is then visible to see if there is some larger shorting happening producing that acrid smell which has kept me from wanting to drive the car.

That was the reason I queried water incursion.

On a side note not to thread jack the only easy fix I considered for the cause of this melting smell was the blower resistor burning the microfilter which I've documented happening before.. easy to check when I have time..

[Mr. E28]

Thanks for the heads up on the ballast/tach issue. Going to try moving them and wrapping them with foil. I've got a resistor on the way, and the seller of the reman lkm is sending another one out, so fingers crossed. If I still have problems after that one, it's back to the drawing board I guess. I did notice something tonight though. While the car is off, repeatedly flipping the lows on and off causes no issues. When I start the car, they either come on right when I hit the switch, or maybe 5-10 sec later.

[Mr. E28]

Well the second LKM didn't fix anything. What is happening now is the lows seem to be only turning off as I accelerate from a stop, then turn back on as I am slowing to a stop. If the car is sitting still, they are fine. I'm moving on to checking grounds. I wonder if a connection to the fuse box/LKM is loose.

[jehu]

I dread such electrical issues.. My dome lights vanished a few days ago... they started to glow tonight then came on ... for a while then went away completely again... woo hoo..

[Mr. E28]

I dread such electrical issues..

It's so annoying because it's mimicking a known issue to a tee, but nooo, that's not the problem. Why couldn't it be my heated seats, sidemarkers, wipers, or anything else that doesn't keep the car from being usable for half of a day?!