1984 R80 G/S tail light wiring issue

I am resurrecting a 1984 R80 G/S that sat for about 10 years. The previous owner died unexpectedly, so I don't have information on what issues the bike was having when he left our planet. My tail lights weren't working when the bike was running. I checked the fuses located under the tank. I saw in a schematic in my Clymer's book (page 780) that the solid gray wire should leave the ignition switch and go to that fuse. From there, two wires that are gray with black stripes exit. One goes to the tail light, and the other goes to the parking lamp and instrument lights. What is odd to me is that the schematic shows that the gray wire will only be "hot" when the switch is in the parking light position, but not the running (fully on) position. Well low and behold that is exactly how mine works. The tail light is lit in the parking light position, then promptly goes out when I turn the key fully on, but the headlight works just fine -- both high and low beam. I looked at some other schematics, and see that some other models have a headlight relay, and a gray wire comes off of it, and heads to the fuse box. That makes sense to me. But my model doesn't have a headlight relay, or a second gray wire going to the fuse. I can't figure how the tail light is ever to be on when in the regular running mode if my ignition switch is right, and the wiring schematic is right.

A friend tells me that a simple diode from the yellow (headlight) wire to the gray wire will correct the problem, but I'm still mystified on how the system was designed to work, if that pretty Clymer's schematic is correct.

Has anyone dealt with this problem, or know how it should work?

Thanks very much for reading.

Welcome to the forum! The link in my signature line has this wiring diagram for the '81-'84 R80-R100:

http://www.stephenbottcher.net/BMW/wiring_diagrams/1983_R80RT_color_wiring.pdf

It's hand drawn but hopefully reflects reality. Does it match what you've been looking at? I see the gray/black wiring going through the fuse and then a gray wire to a relay. Does your relay have the same pin out or is it a substitution without the proper functions? That's where I'd look.

The connection is made through the ignition switch, the parking lights (front small bulb and rear tail light) are the only things turned on in the park position and then the ignition and headlight are added in the next position (it depends on the ignition switch as the Euro ones allow the bike to run without the headlight and the North American ones have fewer positions so that the headlight is always on with the ignition - not sure what year they started doing this but my 1990 R100PD was like that until I installed the Euro ignition switch).
Wiring diagram here http://bgoodsoil.smugmug.com/photos/487529893_zqxze-XL.jpg

Nope, unfortunately the diagram in your link (which is a very beautiful color schematic, not hand drawn) is like the other type I mentioned in my original post. It has TWO solid gray wires going to the fuse. One from the ignition switch, and one from a headlight relay. My bike doesn't have a headlight relay, or a second gray wire going to the fuse.

I know it is hard to read (not colored) but in the resources link you supplied at the very bottom of your post there is a link to schematics that Stephen Bottcher was kind enough to put up specific to the 1980-1986 R 80 G/S. It is like my bike, with only one solid gray wire going to the fuse, and no headlight relay at all. If you look at it, remember that Gray is abbreviated GR. It looks like the schematic I have in my rider's manual. Clymer has it colored on pages 780-781, at least in my copy of the book.

Thanks for looking,
Mystic Daytona

Paladinwest has it right. The parking lights come on and then stay on when the ignition is in the run position. It takes place in the switch. Coming off of the yellow wire would be a mistake as it would only come on with the low beam an go off with the high. You might try checking the switch connection and cleaning the switch contacts.

gray wire

This is somewhat simple. The ignition switch will put power to the grey wire in the park position. So if, after you're sure that the grey wire is on the correct terminal on the switch, you can pull the grey wire and run a test light from there to ground.
Turn the switch to park and the light should light. Since the switch should keep power to the grey wire in the on position, turn the switch to on. The light should stay on. If it doesnt, then you have a bad ignition switch.
Since you say that with the switch in the park position, you have headlight parking light and taillight working, then that's what I'd look at first.
In the big picture of BMW wiring, a solid green and a solid grey wire are powered by the ignition switch. These wires go into the fuse powered. The green wire and the grey wire come out of the fuse as fused wires. The grey/black wire should only provide power to the taillight and parking light, and guage illumination lights on some models.

To both Gary and Paladinwest:

I've seen this schematic, too, and it makes sense. But here's the problem: Again, referring to the Clymer's schematic, it shows that the gray wire (which is on the post #58) is only hot in the parking light position, not the fully on position. There isn't a dot above the gray wire to show it is connected in the fully on position. Looking at the schematic that Paladinwest sent, yes, it has the dot in the fully on position for the gray wire for the US version. But my ignition switch doesn't operate like that. Post #58 goes dead once you move the key to fully on. That's just like the Clymer's schematic shows it, so I'd be surprised if my switch is bad in the same configuration that their schematic shows. It seems to me that #58 should stay hot, just like the schematic that Paladinwest put up.

R80G/S were produced with two different ignition switches ...

3-position: off/park/ignition

5-position: off/park/ignition/park+ignition/park+headlight+ignition

In the last position on either, park remains on with headlight.

USA bikes were all originally produced with 3-position switch.

I've installed the 5-position switch on mine (there's a matching dashboard)

The 5-position switch is same as used on 1974 (only) /6 bikes.

On 3-position switch, gray attaches to 58, yellow/white to 56, and green to 15. The BMW schematic from the owners manual shows park remaining connected when headlight on.

The diagram that I linked has one gray wire to the ignition switch, but the switch shown is the Euro 5 position switch. On my 1990 I have swapped from the 3 position to the 5 position without changing the wiring. I have also replaced the ignition switch with a toggle switch on a 1989 GS when my friend lost his ignition key on the way to Fairbanks. I did a fair amount of digging when I was looking for the factory method of turning off the headlight and the ignition switch was the most common way, particularly on GS's.
It's always possible that yours is different, or someone made it different in an attempt to fix a bad ignition switch.

Don't consider Clymer correct in all respects. People have pointed errors in it before, as well as Haynes, and even BMW's manuals. In the end, if you know how things are supposed to work, then that might be the way to proceed regardless of what Clymer says.

20774 said:

Don't consider Clymer correct in all respects. People have pointed errors in it before, as well as Haynes, and even BMW's manuals. In the end, if you know how things are supposed to work, then that might be the way to proceed regardless of what Clymer says.

Click to expand...

This, plus recognize the fact that it isn't always obvious on switches and relays which terminal a particular number label refers to. I wouldn't make a first guess that the OP's switch is internally broken, but would instead guess he doesn't have wires on correct terminals.