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R90/6 electrical question

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schrader7032
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Re: R90/6 electrical question

Post by schrader7032 »

OK, I'm going to go way out on a limb and step off into the unknown!! I'm seeing in the handlebar start button two terminals, a 50 and an 85. I think the 50 is a red herring, but the 85...when you push the start button, you basically send power to 85 on the headlight terminal board which is connected to terminal 85 on the starter relay. What happens at this point is that that closes the relay and lets power through to the other side at terminal 87. There are two connectors at 87, one going to our mystery 50. The other 87 wire goes to the starter motor at terminal 50/30 and I believe pulls the contacts closed for the solenoid and full power 16gage wire is pulled to turn the starter motor.

So our second wire off of terminal 87 goes to the headlight bucket to terminal 50 and it stops there. What happens when you hit the start button in the headlight shell? Don't all the indicators go dark, I presume to allow all power, etc., to be focused on starting. The headlight also turns off...that might be related in a different way in terms of the headlight relay.

Could this terminal 50, which has power on it when hitting the start button, have something to do with somehow turning off power to the speedo pod and all the lights? That would make sense also for US-only bikes probably. Not sure how that would happen, though. :?:
Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2
Fast. Neat. Average. Friendly. Good. Good.

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sblaylock
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Re: R90/6 electrical question

Post by sblaylock »

srankin wrote:
Fri May 06, 2022 4:14 pm
Scott, the color schematic you have posted for the 75,76 bikes is the same pattern as the schematic Webmore posted at the very beginning of this thread, his was in B&W yours is in color.

Did you look at the schematic I posted where a black wire is clearly shown going from 87 on the starter relay to 85 on the light relay? It is marked US only?
...
Hi St,

I did see that original one but figured the color one would be easier to read... and understand. I also wanted to point out that the 74 /6 is different and doesn't have said wire in question. Kurt may be on to something as the 74 /6 does not shut all the lights off when the starter is pushed.

Scott.
Scott Blaylock
Stoney Peak BMW Service
Victoria, BC. Canada
BMW Classic and Vintage Motorcycle Service and Restoration
service@stoneypeak.com

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sblaylock
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Re: R90/6 electrical question

Post by sblaylock »

Brad,

Does your Start Relay have a bound 87 terminal i.e. two spade terminals for 87 or an 87 and 87a like the one shown in the wiring diagram I sent?

The way I understand it is these work differently in that the 87a is a change over type relay, where the 87a terminal is connected to terminal 30 when the relay is not energized and connected to terminal 87 when it is energized.

The bound 87 relay, as shown in the wiring diagram St sent, would most likely be running to 85 on the Light Relay to kill the lights when the starter is engaged as Kurt had mentioned.

If you have the 87a change over relay the concern would be that 87a would have +12 volts at rest and connecting that to 85 could generate some unexpected blue smoke as the other side of 85 is bound to 31 on the board, which is the ground circuit.

Bottom line, that wire is not "necessary" for the bike to run properly. It looks like it was added for the 75/76 bikes to kill the lights on start. The 74 bikes have a 5 position ignition switch. When I start my 74 R90S I roll it two positions, which brings the dash online, but not the rest of the lights. Once running, I roll it the rest of the way to bring everything else online. As far as I understand, the 75/76 ones have a 3 position ignition. This wire may have been added as the new ignition didn't have a position to enable the start circuit without having the rest of the lights on and add drain on the battery during start. Unfortunately, I don't have access to a 75/76 so I can't confirm this theory.

Scott
Scott Blaylock
Stoney Peak BMW Service
Victoria, BC. Canada
BMW Classic and Vintage Motorcycle Service and Restoration
service@stoneypeak.com

wbmoore
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Re: R90/6 electrical question

Post by wbmoore »

Hi guys…I’ll try to answer all. Kurt: I woke up this morning to a nice explanation from Snowbum. Thanks for the suggestion. His best, very educated guess is the 0.75 SW wire was, at one time, used to control the headlight relay while the starter was being used. Throughout the span of the /6, the harnesses were different in Europe and the U.S.A. After a brief bit, the relay was changed and this wire could have become redundant. sblayloch: My relay has EIGHT spades..however 85 is single, 86 is single, but the two 30 spades are married, the two D+ are married and the two 87 spades are married. Your answer agrees with Snowbum. dbclemmens: thanks-visual proof. St.: exactly.

So……long story short: I don’t need that 0.75 SW wire that starts at starter relay#87 and goes to nothing in my bike. Thanks to all participants. You are a bunch of guys that do not give up ! THANKS. Brad Moore.
Brad Moore
1960 R69; 1975 Norton MKIII; 1976 R90/6; 1992 K75S; 2000 Hayabusa
Big Bar, Northern California

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srankin
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Re: R90/6 electrical question

Post by srankin »

Thanks to Kurt and Scott, you went beyond just locating the position the wire was supposed to go to but gave reasons for its existence in the first place. This was confirmed by Snowbum (thank him as well).

I am sorry, I was never trying to figure out WHAT the wire was for or what it did, I was looking for where it went. After that, I would figure out what it did or did not do. Figuring out were it went was the original question, LOL.

Now that it is confirmed where it went or such, I can see exactly how it was or is supposed to have functioned, and yes in the US models why it was different than the Overseas bikes. Also, why the earlier versions of the bikes did not have it.

LOL, answering questions or trying to troubleshoot issues in a forum sure is not the best way to do things but it is better than nothing. I would rather have the person come to my garage or me go to them but, that is not always the case.

So now we all have been educated, good luck on the conversation, send pictures, most importantly enjoy the ride. Thanks again to all. St.
Owner of a 84, R80RT and 78, R100RS

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