1977 R100RS Instrument Cluster mismatch

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kingcowie
Posts: 28
Joined: Wed Oct 28, 2020 1:29 pm
Location: Wollongong

1977 R100RS Instrument Cluster mismatch

Post by kingcowie »

I recently bought a barn find r100rs which had been stripped down and i have been going through the wiring to check for furphies and i have found a few.
The major one at the moment is that the instrument cluster supplied with the bike does not match the instrument cluster plug as seen in the photo. The instrument cluster is the electronic tacho, green turn signals at the top and high beam at lower light.
The other give way is that the bike had brake fluid level switches front and back but were disconnected as the instrument cluster has no brake fluid light.
And i was chasing down why the indicator light does not come in instrument cluster,
indicators work - check
KBL output from turn signal -check
Instrument light indicator light good health - check
Output to the Instrument light indicator light - check
But what i found is that the other side of the indicator light circuit male pin 11 has no mating female 11 and hence not grounded.
The instrument cluster pins dont match the connection plug.
Is there a wiring diagram or the like for how the cluster and tacho should be wired and also how do i work out what instrument cluster plug i need. I have gone through the std wiring diagrams but missing electronic tacho details.

Thanks Shane
Attachments
IMG_5809.jpg
Instrument Cluster Layout Connector and Board.jpg
Shane
Wollongong, Australia
71 R75/5
64 R50/2 Project
77 R100RS Project

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srankin
Posts: 163
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA

Re: 1977 R100RS Instrument Cluster mismatch

Post by srankin »

I am a bit confused, are you saying the instrument cluster you have in your picture is the one you have NOW for the bike? The instrument cluster you have in your photo is for a newer bike not your 77. I am not sure the year BMW changed perhaps 81?
The correct cluster will have as you say, the high beam indicator light (blue) located in the tachometer. It will also have an indicator light in the center for brake failure (Yellow).

To be honest, I would not attempt to try to rewire to fit this housing/combination. You will most likely drive yourself batty. Not saying it can't be done.

Besides the discrepancy in wiring, there may be a good chance the speedometer you have in this wrong unit may not match the final drive ratio for your bike. I can't see the little number printed on the bottom of the face of the speedometer so I can't say for certain the numbers will match with the final drive on the bike.

Each variation of /7 models have different final drive ratios. For the 1000cc bikes, the lowest ratio belonged to the RS. The naked or S bikes were slightly higher ratio, the RT was the highest ratio. With the highest ratio, the engine turned over at less RPM for MPH. Bottom line, a mismatched speedometer can be off a couple of mph or a lot depending on the speedometer you in fact have. Something else to drive you crazy down the road.

Complete clusters are getting to be like hens teeth but they are still out there. I would look for the proper unit to fit your year and model. At least get the proper year with the proper light configuration to match the wiring on your bike. If you can't find the proper speedometer, perhaps you can contact one of the repair shops to ask about changing one to match the final drive on your bike.

I remember you wrote about the brake fluid level system, while I cannot know what the previous owner to you was thinking, I can guess. For some reason, he flubbed up the rear brake master cylinder, removing the float and contacts. this would cause the yellow warning light in the proper instrument cluster to light up. In order to get rid of the brake warning, he changed the cluster. As I say, I can't be sure of this, but kind of looks that way. People do weird things to bikes for weird reasons. There is no end to previous owner mess ups the new owners are stuck with.

To keep your sanity, get a good schematic. I have found the best are available from Euro Motoelectrics or EME. They not only are in color, but have the pin connections numbers on them as well.

Unless the previous owner ripped out and rewired stuff, you will be best off to stick with the proper configuration in the end.

I spent a day working on a friend's Harley on which the previous owner had replaced the speedometer cluster and various instruments with go fast stuff. The problem my friend was having was the charging system was not charging at all. The solution was found after uncoiling and tracing a mile or two of jumping snake wires the previous owner had installed plus had cut in order to achieve his goal of no turn signals, and the go fast instruments. He had removed the charging light bulb from the circuit and had not bypassed it. No lightbulb, no charge. If the PO had a bit of understanding of the bike's systems, he would never have done what he did. Sad part is my friend had a month of riding with nothing but problems before we found the fix.

Things too beware in used bikes; Rats nest wiring, or added on wiring. Wiring not matching factory color codes, missing lights, or not working lights. Anything can be wired or rewired to make it work properly, but the person doing the rewiring better have an understanding of how the systems work before tearing in.

Let me know how you make out, I will check in my spares box, I may have a spare cluster for your bike, not sure I know I have the newer ones. St.
Owner of a 84, R80RT and 78, R100RS

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kingcowie
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Joined: Wed Oct 28, 2020 1:29 pm
Location: Wollongong

Re: 1977 R100RS Instrument Cluster mismatch

Post by kingcowie »

I am thinking that i am starting to understand why he sold it. He has made a number of alterations of stripping down the 77 R100RS see attached and he has got himself into a fix of troubleshooting and fixing the simple issue of the indicator lamp not working.
The production date is 1977/12 Series 2474 Chassis 6088306. The speedo number W=691

Also investigation on the bike there is no entry point for the mechanical tacho cable and also after pulling the front cover off the normal entry point for the mechanical tacho cable is casted closed. See attached.
So maybe this bike was original electro tacho, but it does not explain the plug pin mismatch.

The plot thickens...i think i am missing something simple but it is the haze of days of rat nest work that is clouding my view ..:)
Attachments
IMG_5846.JPEG
IMG_5840(1).JPEG
Shane
Wollongong, Australia
71 R75/5
64 R50/2 Project
77 R100RS Project

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kingcowie
Posts: 28
Joined: Wed Oct 28, 2020 1:29 pm
Location: Wollongong

Re: 1977 R100RS Instrument Cluster mismatch

Post by kingcowie »

The final drive ratio for R100RS was 32/11T 2.91:1.
Shane
Wollongong, Australia
71 R75/5
64 R50/2 Project
77 R100RS Project

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srankin
Posts: 163
Joined: Fri Jul 14, 2017 8:45 pm
Location: Spencerport, NY USA

Re: 1977 R100RS Instrument Cluster mismatch

Post by srankin »

Shane, I am sorry, I have forgotten if you mentioned where you are located, in the US, AU or UK? I see you have a metric speedometer. I am sorry, the number I was explaining to you about is not the same on my Speedometers. To clarify, I will snap some pictures of my system and show you what I mean it beats trying to write it out.

I can assure you, the first picture of the instrument housing you posted is the incorrect system for a 77RS. That in itself explains the plug pin mis match. If the plug itself is factory wiring and has not been rewired, it will not work with that instrument system 100%. Yes, some of the indicator bulbs may be in the same location from 77 to the year that housing fits but there are some that won't.

Don't quote me 100% but I do believe the 77RS had a mechanical tachometer. I haven't been able to cross reference this but I had a 77 R75/7 and it had a mechanical tachometer. I DO know my 78RS has an electronic tachometer. The 77 bike was kind of a one year thing before BMW made changes such as going to disc brakes, from the original drum and going in 78 to snowflake wheels versus the 77 Spoked. If indeed your bike is a 77 and not an early 78 built in 77. (how is it in the end of 2019 the 2020 models are on the sales floor, get my drift?). I would have expected it to have a drum rear yet, you have a disc rear brake. Wonderland gets stranger, I suspect while your bike may have been built in 77, it may in fact be a 78. Or, the previous owner changed the rear end out for a disc brake and put on snowflake wheels.

Granted, I am not an expert and I hope someone will jump in here and tell me I am on there right track or very wrong. In saying I am wrong. there may be 77 RS bikes out there with disc brakes on the rear and electronic tachometers.

Okay, I am going on and on. If your bike is a 78 and not a 77, the port in the front cover for the timing cable will be closed off. I will try to get my butt in gear and get a picture of my 78 front cover to confirm this.

To be honest, you may not have as many problems you think you might have. IF the wiring harnesses don't show any signs of non BMW wiring,(wrong gauge wire, sloppy connections, spliced in wires, and so on) by finding the correct instrument cluster to fit your bike as well as fixing the float on the rear brake master cylinder, you may find the wiring is fine. Correct wiring won't work with mismatched parts. The danger is when like my friend's Harley, the PO "modified" things and hacked up the original wiring harnesses.

Kurt, I am waiting for you or Mac to jump in with your knowledge of bike models and cross references to help out.

Cheers, St.
Owner of a 84, R80RT and 78, R100RS

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kingcowie
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Location: Wollongong

Re: 1977 R100RS Instrument Cluster mismatch

Post by kingcowie »

St,
Thanks for your input. Just a couple of points
I am in Australia.
The engine and frame numbers match.
I am sure it is the original wiring but with modifications at the ends ie disconnect the brake fluid level front switch, disconnect the buzzer, removed voltmeter and clock etc.
The instrument claster (female) wiring does not match the instrument cluster. The oil, gen, high beam, instruments lights all are wired correctly and function BUT the indicator lamp does not work. The power to this lamp is run from the turn signal relay/ switch with a KBL black white cable and is connected correctly but the ground side of this lamp stops at the male ( Pin) side of the instrument. The matching female on the plug does not have a wire running to it (blank).

But the other mystery is that their is no provisions for a mechanical tacho cable the entry point is cast shut (see Photos).

But the bike has brake fluid level switches so suits the older instrument with the tacho light but cant make this work as no provision for the tacho mechanical cable.

Mystery continues..

S
Attachments
IMG_3487.jpeg
IMG_5846.JPEG
IMG_5612.jpeg
Shane
Wollongong, Australia
71 R75/5
64 R50/2 Project
77 R100RS Project

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schrader7032
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Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX

Re: 1977 R100RS Instrument Cluster mismatch

Post by schrader7032 »

About all I got is that I agree, the '77 was a mechanical speedometer and '78 went electronic. I don't think I'd seen chrome bezels on the instruments before...maybe that's what's under the black plastic "hoods" that come on them.
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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srankin
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Location: Spencerport, NY USA

Re: 1977 R100RS Instrument Cluster mismatch

Post by srankin »

Hello Shane, As I have said, the instrument cluster you have mounted on the bike is the wrong one. That is why the plug does not match up. Until you get the correct instrument cluster, you will be chasing your tail. If you insist on keeping the cluster you have, your only option will be to rewire the main instrument plug as to align the properly placed pins to match up with the wrong cluster. I seriously advise against this.
The main plug going into the instrument cluster, is part of the main wiring harness.

As for the rear master cylinder harness, it is a sub harness that plugs into the main harness. It is also possible the front master cylinder switch is a separate harness.

The clock and voltmeter are a separate harness plugged into the color coded main board inside the headlight shell. That harness can be removed without messing up the main harness or the left and right control harnesses. If the previous owner didn't remove the clock voltmeter harness completely, there will be a bundle of loose wires inside the headlight shell.

I am beginning to think you don't have a 77 model bike but in fact a 78 early release bike. I have found no evidence of 77 year bikes having snowflake wheels with a rear disc brake. Only the 78 and newer bikes had them. The 78 bikes also introduced electronic tachometers. As such, you will not have a port in the front engine cover for a tachometer cable. But again, with the wrong instrument cluster, the tach may not work because the pins for the main plug don't align with the cluster.

I will make an effort today to get out the camera and take some pictures of my 78RS to see if maybe I can explain things better. I don't think your wiring is messed up, it may be missing a couple of sub harnesses and of course it won't match up with incorrect parts but unless there are obvious signs of someone hacking it or adding to it, It should be fine.

St.
Owner of a 84, R80RT and 78, R100RS

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schrader7032
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Joined: Fri Oct 27, 2006 3:00 am
Location: San Antonio, TX

Re: 1977 R100RS Instrument Cluster mismatch

Post by schrader7032 »

Plug your 7-digit VIN into this and see when the bike was built:

http://www.bmw-z1.com/VIN/VINdecode-e.cgi

My '78 R100/7 was built in September 1977, so definitely an early '78 model. I've heard that BMW likely began substituting a new harness capable of interface with the electronic tach prior to the 1978 models.

Here's the picture of the light stack on my '78.
Attachments
speedolights.jpg
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

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srankin
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Location: Spencerport, NY USA

Re: 1977 R100RS Instrument Cluster mismatch

Post by srankin »

So, I am back onto the mystery and chase to get this all sorted. Kurt, you commented on the trim rings on Shane's cluster, not a problem, they are some aftermarket rings substituted by the PO as a replacement of the rubber ones that are stock.

I am going to see how my picture download skills are and try to use the pictures I took of my RS to help out.

I may end up doing this picture download in different posts to this thread rather than cramming them into one post. I hope it makes it easier to follow my trail.

So here goes the first picture; This is the correct instrument cluster for your bike Shane,
Correct cluster
Correct cluster
Note as Kurt and I have said, there is a brake warning light in this cluster. Any cluster other than this will not work on your bike unless you rewire the plug from the main harness.

This picture is off my 84 bike and is the same one or similar to the one you now have Shane, It is incorrect for your bike.
Wrong cluster
Wrong cluster
There is no brake warning light and the high beam indicator is moved from the tachometer to the center. As there are changes internal to accommodate this, it will not work 100% with your bike.
Owner of a 84, R80RT and 78, R100RS

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