Headlight Help!

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songzunhuang
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Headlight Help!

Post by songzunhuang »

Not too long ago I was having headlight issues and I was able to fix them. However, a parasitic draw which killed my battery seems to have made a new headlight behavior appear. I recharged the battery an then this strange behavior started. It's so weird that I am just scratching my head. I am hoping someone can help.

Basically, my low beam headlights will only come on when I have the high beams on.
When I turn on my low beams, all the side marker and tail lights are on, but I have no low beam headlights.

If I turn on my high beams, then my low beams come on, but I never have high beams. So now I drive around at night with my high beams on in order to have any lights at all. Also, my fog lights operate as expected when I am driving around with my high beams switched on ( in order to have low beam).

I have checked all my fuses and relays and they appear to be operating as expected. The low beam relay clicks when I turn on the headlight switch and the high beam relay clicks when the high beam is activated from the steering column stalk. Help!
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Song Huang
1984 633CSi
Last 7 of VIN: 6997383
plip1953
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Re: Headlight Help!

Post by plip1953 »

Aren't these kinds of odd behaviour generally down to a bad earth somewhere?
Last edited by plip1953 on Mon Nov 28, 2022 8:14 am, edited 1 time in total.
Phil
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songzunhuang
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Re: Headlight Help!

Post by songzunhuang »

plip1953 wrote: Sat Nov 26, 2022 1:01 pm Aren't these kinds of odd behaviour generally down to a bad earth somewhere?
I guess that's possible, but what has me totally baffled is that everything was working a few weeks ago. Then I had my battery go dead from a parasitic draw (which I still haven't found). When I recharged the battery, all this weird behavior appeared. I can't think of any reason why recharging a low battery would cause this. Everything else electrical i fine in the car. Anyhow, I while pondering a solution, I thought I'd reach out to see if anyone had ever encountered this.
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Song Huang
1984 633CSi
Last 7 of VIN: 6997383
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hornhospital
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Re: Headlight Help!

Post by hornhospital »

Check the unloader relay. It temporarily turns off your high-draw items like headlights while cranking the engine. I've never had one fail, but it could possibly be part of the problem with both the wonky headlights and the phantom battery drain.
Ken Kanne
'84 633CSi "Sylvia"; '85 635CSi "Katja";'85 325e "Hazel Ann"; '95 M3 "Ashlyn"
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Re: Headlight Help!

Post by songzunhuang »

hornhospital wrote: Sun Nov 27, 2022 8:44 pm Check the unloader relay. It temporarily turns off your high-draw items like headlights while cranking the engine. I've never had one fail, but it could possibly be part of the problem with both the wonky headlights and the phantom battery drain.
Ken, I pulled the relays (K5 & K7) and checked them both. They appear to be ok. So I decided to swap out K5 and then K7 with a spare to see if anything changes. When I did nothing happened. I then looked at my fuses and 1 was blown. Not sure if the swap caused it. So I swapped things back and replaced the blown fuse. I checked the other headlight fuses and they (2, 13, 14) were all ok.

Then it got worse. When I pull the headlight switch on, I hear no click of a relay. If I activate my high beam, I do hear a click. However, none of my headlights work now. Sigh, it's just getting worse. Looks like I m driving my other car again until I can figure this out.

Still, I'm all ears if folks have other ideas.
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Song Huang
1984 633CSi
Last 7 of VIN: 6997383
kronus
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Re: Headlight Help!

Post by kronus »

Try directly closing the connections necessary to turn the low beams on. You can do this at the fuse box and the switch, which would let you isolate which part of the circuit has a problem. You do need an ETM, but maybe you have one already.

Or, swap out the headlight switch. I have one in a 1980 car if you’d like to try.
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Ralph in Socal
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Re: Headlight Help!

Post by Ralph in Socal »

I agree you should check the headlight switch. Unfortunately later series 2 switches are different from series 1 so Dmitry can't help with his. I do have several spares and they are known to fail. However spraying contact cleaner may help so try that first.

The suggestion about bad grounds is also a distinct possibility. The turn signal/high beam activator switch Is also problematic so spray that with contact cleaner also

Lastly, most exterior lighting goes through the hazard switch so check/spray that and get a spare also

Ralph
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Re: Headlight Help!

Post by songzunhuang »

Ralph in Socal wrote: Mon Nov 28, 2022 8:00 pm I agree you should check the headlight switch. Unfortunately later series 2 switches are different from series 1 so Dmitry can't help with his. I do have several spares and they are known to fail. However spraying contact cleaner may help so try that first.

The suggestion about bad grounds is also a distinct possibility. The turn signal/high beam activator switch Is also problematic so spray that with contact cleaner also

Lastly, most exterior lighting goes through the hazard switch so check/spray that and get a spare also

Ralph
Ralph, I had a chance to check a few things and here are my observations. I hope they can reveal some clues.
First, my hazards seem to operate just fine.
Is the turn signal/high beam activator switch built into the the stalk? I replaced that with a new one a while back when I broke the tab for the self cancelling part of the signal. Although a possibility I wouldn't suspect that part as much.

I found a table in the Bentley manual about a Headlight Circuit Electrical Test. After performing the test, I found an anomaly. The question is, does it point me to the headlight switch? Here's what it says for the low beam relay socket.

* 30 and ground = battery voltage. I do not get this.
* 85 and ground = continuity with headlight and highbeam switch off. Confirmed.
* 86 and ground = 12v with Ignition on and headlight switch on. Confirmed.
* 87 and ground = continuity. Confirmed.

So the one test that fails is the *30 and ground. I never get battery voltage there. Does that indicate a switch failure? I looked at the schematic for the headlight circuit and I can't say for sure as it isn't clear to me that 30 runs through the switch, but it looks to me that that *30 on the low beam is connected to *87a on the high beam, which is linked to *30 on the high beam and then connects to power. See the red circle in the diagram below. Could I have the wrong High Beam relay? I guess I'll have to pull it and test. Hoping some more experienced folks can chime in. Here's the schematic below.
Red circle is the bridge between relays.
Red circle is the bridge between relays.
Headlight-Help-bigcoupe-com.png (555.28 KiB) Viewed 949 times
Finally, my headlight switch has 2 plastic tabs that secure the connector to the edge of a PCB board. Is that a series 1 or series 2?
Attachments
Headlight circuit schematic.
Headlight circuit schematic.
Headlight Schematic.png (537.34 KiB) Viewed 1232 times
Last edited by songzunhuang on Mon Jan 23, 2023 7:03 pm, edited 1 time in total.
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Song Huang
1984 633CSi
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Re: Headlight Help!

Post by songzunhuang »

wfwright2 wrote: Wed Nov 30, 2022 3:27 pm Song, Ralf
Jumping into the middle of this, sorry. Retired EE following in the periphery.
Did you do the low beam relay socket terminal 30 check with the high beam relay in place? If yes, is there battery voltage at the terminal 30 for the high beam relay. If battery voltage is present that points to a faulty high beam relay, if none then an issue with the power distribution within the fuse box.

Willie
Willie, thanks for chiming in. I was lying in bed last night thinking the exact same thing as you! I checked with the high beam relay in place and wasn't getting voltage. From the schematic, that means that in order to get voltage on 30 for the low beam relay socket, I must have voltage on 30 on the high beam relay and the high beam relay must have continuity across 30 and 87a when static. That was the next thing I was going to check.

Is there such thing as a 5 prong relay that doesn't have continuity across 30 and 87a at rest? It occurred to me that I replaced the high beam relay with a new one thinking that would eliminate that variable. I'll have to wait a few days before I have time to check.

I also realized the Bentley manual wiring diagram (not exactly for my model) and the one I posted for my 84 633csi are NOT the same. That was a source of confusion for me as well. I hope we are one step closer to solving this.
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Song Huang
1984 633CSi
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Headlight Issue Solved!

Post by songzunhuang »

OK, in a slap my forehead moment, I realized that the high beam relay is a 5 prong switchover relay not a normally open. What does this mean? A switchover relay has an 87 and 87a terminal. There is continuity on 30 and 87a. When energized, the continuity changes over to 30 and 87.

I had replaced my high beam relay with a new relay, but but it was a normally open relay! This means that when energized, BOTH 87 terminals have continuity with 30. This makes all the difference.

Studying the wiring diagram, I realized that voltage is carried from 30 to 87a in the high beam relay and that voltage from 87a connects to the low beam relay pin 30. Having the wrong high beam relay caused all kinds of bad behavior. ](*,)

Now, I blew a few mote 7.5 amp fuses in the process so I inspected and reinstalled all my headlight connectors. After that, everything worked! \:D/

I can't believe my stupid mistake thinking all 5 prong relays were the same.
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Song Huang
1984 633CSi
Last 7 of VIN: 6997383
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Re: Headlight Help!

Post by dks »

Hi Song,

Just saw your post. Glad you've got it sorted - I had a similar problems couple of years ago.

I think your headlight setup has a two filament low beam globe (one for dipped and one for high beam) and a high beam globe. As well as turning on the high beam the K3 relay switches out the dipped filament and switches on the high beam filament when high beam is activated.

My car has a single filament low beam and the K4 relay pin 30 is hot at all times. So the K3 and K4 relays are not wired together.

I hope the headlight wiring of your car the same as the ETM - mine isn't.

Makes things quite confusing


...Dave
'87 635
'84 323
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