Rogue Wire

[lukasgrech]

As I was toothbrushing the years old muck from the bottom of the engine, I discovered a lone wire on the left side of the engine (pictured). I am assuming due to its location and colour that it is an earth connection. It also looks like it has been deliberately snipped, not accidentally torn off.

What is this wire, and what should it be connected to? All the electrics on the bike work fine so I am wondering what the purpose of it may be.

[steve hawkins]

You and me both.

Could have been an aftermarket accessory, that is no longer fitted.

Or a workaround for an issue that is no longer an issue.  

Why they could not have just undone a single bolt instead, is beyond me.

Rev. Light

[steve hawkins]

Having said that I have one fitted to my R100.

 

Let me look at my circuit diagram and get back to you

Rev Light

[steve hawkins]

It might be from your neutral switch, or even your oil pressure switch.

You need to get a manual and look at the loom section leading down the frame tube to these switches.

It might be earthed somewhere else, as your neutral light is working?

Does your oil pressure light work?

Rev Light

[arvo92]

You guys made me curious enough to get myself up and walk to my garage in half 11 pm as I knew I had the same wire but connected.

The wire comes from the same tube as the neutral switch indicator two wires do. So one black hose has 3 wires in total and this one on the picture is the third one.

As Steve mentioned before - do you have the neutral switch indicator light working on the clock?

[lukasgrech]

Cheers.

Yeah all the switches are functional. I would not be surprised if it is from some accessory that has been removed, or perhaps indicator buzzer which should be on this year bike, but apparently is not on mine. From what I see from my bike it looks like it's been a bit of a guinea pig.

Another anomaly I've come across, is my speedo. On the speedo (120MPH version) it says W 1441. Now I've trawled this forum and various sites, and nowhere have I found reference to a speedo with this ratio on it. Maybe I've not searched hard enough, but I'd like to eventually swap the big instrument cluster with a small speedo such as this one:

http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-electronic-parts-mini-black-face-led-speedo-speedometer-25-7032b.html

But I can't seem to find one that fits my ratio. Any tips?

[lukasgrech]

Arvo, the wire you mention that comes out of the same tube is the one that is pictured, but connected. So I have 2 wires to your one.

[georgesgiralt]

Hello !
The torn wire is the grounding for the neutral switch on the tranny.
The oil pressure switch does not, normally, get a brown wire on it (as it gets it's ground from the engine case to which it is bolted).
The two wires, one from the neutral switch and one from the pressure sensor run along the frame to the battery box where there is normally a small connector to get them back into the main wiring harness. This small harness is still sold new by BMW and not so expensive. But maybe you lack the small connector too...
So your wiring had been messed up .....  

[Barry]

Another anomaly I've come across, is my speedo. On the speedo (120MPH version) it says W 1441. Now I've trawled this forum and various sites, and nowhere have I found reference to a speedo with this ratio on it.  

That's a speedo off a 35HP R45.

The speedo ratio is the number of cable revolutions for 1 mile travelled and therefore the correct ratio depends on which final drive you have.

[nhmaf]

I've got one of those ground wires as well - the intention is that the German engineers didn't want to rely on the anodized surface of the engine block and the gearbox making a good electrical connection, or rely on the bolt threads that hold them together to carry current.   In many instances, the wire is redundant in functionality, though from a purely electrical perspective, it is/was the *proper* way to ensure ground commonality in the electrical system.

So, unless your final drive is stamped 35/9  it seems someone has replaced your speedometer with a recycled one from an R45.    Your speed and odometer readings must be off by quite a bit (about 9%) otherwise.

[montmil]

The difficulty in replacing Airhead speedos with aftermarket units is finding a product that will: 1) have the correct ratio, and 2) Adapt to the gearbox drive.

if you would accept an additional 0.5" in diameter, the Dime City digital unit is perfect. Evens has a machined aluminum 'plug' for the road speed portion of the gauge that fits the Airhead gearbox.

You just have to get past the price. http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-electronic-parts-mini-black-acewell-4553-digital-motorcycle-speedo-speedometer-tach-tachometer-19-4553-bk.html

My 1983 R65 has the Dime City in black. My '81 R65 and the '78 R100S bought carry the TrailTech vapor digi gauges.

[steve hawkins]

Yep, Tony, my brother, is running one of those on his r65.  Very trick!

Rev Light

[lukasgrech]

My final drive has 31/9 stamped on it, but I cross checked my speeds with the gear/RPM - MPH conversion table in the FAQ section, and the speedo readings are accurate. The PO must have had the speedo calibrated, odd that he wouldn't have just found a replacement R65 speedo.