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why does the tail light quit working when the turn signal stops working?

Roguetek

New member
I'm wondering why this is so, as it doesn't seem like a good idea.

I can't think of any reason why the tail light/brake light should be wired into the turn signal relay, and yet, sure as gravity, when my turn signal relay dies (Which happens with annoying regularity. I'm averaging a relay a year), my tail lights quit working.

Why is this so?

EDIT: A brief perusal of the wiring diagram reveals no clues either. In fact, I don't see where the wiring connects the two, which confuses me even more.
 
What bike are you talking about? Probably a research of the appropriate wiring diagram might have some clues.
 
The common lighting connection on the back end of a /7 (or any airhead I am familiar with) would be the brown wire, which is ground.
 
I can't think of any reason why the tail light/brake light should be wired into the turn signal relay

And it shouldn't be.

Since you started the Sourcing Wire thread, I'm gonna go out on a limb and guess that your wiring harness is a mess...

If your TAIL LIGHT is going out when your T/S RELAY fails it must be receiving power from it - and it should not be.

The TAIL LIGHT circuit (main block terminal #58 (Black/Gray)) also powers the INSTRUMENT LIGHTS, the CLOCK and VOLTMETER lights, and the PARKING LIGHT (in the head light. Do these lights also fail when the T/S RELAY goes south?

A BLACK/GRAY wire should be connected to terminal #58 ON THE TAIL LIGHT. If it is not, what color is?

... my tail lights quit working.

You only have one tail light, right? The turn signals are not both steadily illuminated at the same time... ? Correct?

edit - See if your TAIL LIGHT terminal #58 is somehow connected to T/S RELAY terminal #49a (not 49). 49a (GREEN/YELLOW) powers the turn signal switch on the handlebar perch.

I hate burning up the bandwidth, but it helps to see the diagram.

78r100wire.jpg
 
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I'm going to do a more in-depth digging, but as of right now..

1. the tail light/brake light fail when the blinker relay is removed.

2. the blinker will only blink for so long, before it stops blinking for a little while. If shut off, it starts working again in 5-10 minutes.

3. The blinker indicator will fail if left on for too long. THis too, resumes function, if left off for a while...

I will post more, as I have more.
 
I would also be looking into why your t/s relays keep getting killed (which is different than just "dying".) Something is not right there- if i think back on it, i have had exactly ZERO t/s relays die on a m/c in the last 35+ years.
 
1. the tail light/brake light fail when the blinker relay is removed.

The TAIL LIGHT and BRAKE LIGHT should receive power from two separate terminals on the main contact plate inside the headlight housing. If they do not come on when the RELAY is removed it is because they are receiving power from the RELAY circuit - which is incorrect.

The TAIL LIGHT > from terminal 58 (gray/black wire; on the contact plate in the head light) which is energized by the gray wire when the ignition switch (terminal 58) is turned on.

The BRAKE LIGHT > terminal 15 (green/black wire; on the contact plate in the head light) which is energized by the GREEN wire when the ignition switch (terminal 50) is turned on. The GREEN/BLACK wire feeds the front and rear brake light switch - the wire(s) coming out of the two switches are GREEN/RED and go to the BRAKE light terminal 54 in the housing.

2. the blinker will only blink for so long, before it stops blinking for a little while. If shut off, it starts working again in 5-10 minutes.

Your RELAY is overheating and failing (again).

3. The blinker indicator will fail if left on for too long. THis too, resumes function, if left off for a while...

The INDICATOR is fed directly from the RELAY by a BLACK/WHITE wire which is connected to terminal KBL on the RELAY. If the INDICATOR LIGHT is failing it's because the RELAY is failing.

The TAIL LIGHT circuit (main block terminal #58 (Black/Gray)) also powers the INSTRUMENT LIGHTS, the CLOCK and VOLTMETER lights, and the PARKING LIGHT (in the head light).

Do these lights also fail (go out) when the T/S RELAY goes south or is disconnected?

Have you opened up the headlight housing and taken a look at the contact plate to verify correct connections per the wiring diagram?
 
And it shouldn't be.

Since you started the Sourcing Wire thread, I'm gonna go out on a limb and guess that your wiring harness is a mess...

If your TAIL LIGHT is going out when your T/S RELAY fails it must be receiving power from it - and it should not be.

The TAIL LIGHT circuit (main block terminal #58 (Black/Gray)) also powers the INSTRUMENT LIGHTS, the CLOCK and VOLTMETER lights, and the PARKING LIGHT (in the head light. Do these lights also fail when the T/S RELAY goes south?

A BLACK/GRAY wire should be connected to terminal #58 ON THE TAIL LIGHT. If it is not, what color is?



You only have one tail light, right? The turn signals are not both steadily illuminated at the same time... ? Correct?

edit - See if your TAIL LIGHT terminal #58 is somehow connected to T/S RELAY terminal #49a (not 49). 49a (GREEN/YELLOW) powers the turn signal switch on the handlebar perch.

I hate burning up the bandwidth, but it helps to see the diagram.

May I ask where these colour diagrams are from? I have the B/W ones from PowerBoxer.de linked to from Snowbums site but they are blurry and difficult to read. I am looking for schematics like these for my 1982 R100RS.
 
Lew refers to Stephen Bottcher's page which has quite a few diagrams. Snowbum also has some diagrams, but I don't think they're in color, at least not most. The diagram that Lew references above in his post is from a we'll maintained website that is mostly about the 1978 models, but has quite a few other interest articles and brochures. The diagram that was posted is about half way down this page:

http://www.omnilex.com/public/bmw78/

While no diagram is 100% correct, this diagram should be applicable to the '77 /7 in question...except for the cable-drive tach!
 
ok, upon some investigation, it would seem my ignition switch is miswired.

However, instead of having pins 30,30,50,56 ,58 on the back of the switch, I have ( in order) 15, 30, 30, 58, in a row, with pin #56 above the row, in the 11 o'clock position.
 
Symptoms persist.

Blinker blinks very fast, and the blinker light on the dash does -not- light up.

Gauge lights extremely dim.

When in the 'park' position, tail light comes on.

when in the run position, tail light goes out, but brake light works.

Tail light comes back on if you turn the headlight on, and brake lights work.

when the turn signal module is unplugged, tail light/brake light now function.

I"m not sure what I did, but it seems to be working now.

I suspect that my wiring harness is due for a change.
 
You may have a pinched wire somewhere in the harness, or a wire may be connected to the wrong terminal. The only way to really know is to disconnect every wire in the head light and line test them for continuity. Also check to make sure the wires are connected correctly in the tail light housing and that your ground connections (Brown wire) are solid.

It sounds like a daunting task, but armed with a wiring diagram it isn't really too scary. Just take your time. If you have a digital camera take some pics before you start and as you go.

Edit
- you might find this Adventure Rider article helpful. Lots of links to reference photos taken during the project. > http://www.advrider.com/forums/showthread.php?t=371963
 
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ok, upon some investigation, it would seem my ignition switch is miswired.

However, instead of having pins 30,30,50,56 ,58 on the back of the switch, I have ( in order) 15, 30, 30, 58, in a row, with pin #56 above the row, in the 11 o'clock position.

No, the wiring diagram is incorrect. The Haynes and (newer) Clymer manuals have accurate wiring diagrams for the ignition switch in color. As a clarification, the wiring diagram in the resources section for the /7's is 99% correct and I have only found ignition lock wiring errors. It took me a while to figure that out.

Here is what motobins sells for the igintion lock: http://www.motobins.co.uk/displayfinal.php?q=94700&topsearch=1&go=GO

which has correct connection pin numbers 15,30,30,58 with #56 above and are the same on my original /7 ignition lock. FWIW, I highly recommend getting the Chicago region owners association BMW electrical manual which has accurate (black and white) electrical diagrams along with some sage advice on trouble shooting airhead electrical problems. Here is that link: http://crbmw.com/rokcart
Good luck!
 
Got a multimeter?

Check the ground on that taillight. Is it grounding THROUGH THE FLASHER RELAY??? I.e., not grounded unless relay is energized (flasher is on)?
 
Electrical System Chart

Some time ago at a national rally, Rick Jones of Motorrad Elektrik was selling laminated color charts of the Airhead electrical system. The chart is 12" by about 18". I don't remember the cost. He suggested that I roll it up and keep it in the frame backbone tube which I did.

These charts are for specific models, not a "one size fits all" situation. The wire colors on the chart are the same colors as on the bike.

I don't leave home without it. WWW.motoelekt.com
 
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