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Topic-icon ‘76 R90S. Electrical issues.

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3 months 5 days ago - 3 months 4 days ago #5977 by Blue-1
Replied by Blue-1 on topic ‘76 R90S. Electrical issues.
First-off, I have a /7 which is wired somewhat different than a /6. But the concepts are the similar.

I took a look at the wiring diagram for your bike in my Clymer manual.

* Did you check all the fuses on the circuit board? I suspect you have a blown fuse.
* It appears one side of your starter motor has a constant 12V hooked up to it directly from the battery all times.
* The ground to your starter motor is what gets switched through the starter relay.
* So, all your starter needs to turn, is a good ground from the starter relay.
* With a ohm meter make sure your emergency stop switch is off(open) and not internally shorted. You'll have to take it off you handlebar perch so you can get to the back side to test.
* Make sure your clutch switch is working correctly. shop.maxbmw.com/fiche/NotesParts/61311243403_1_B.jpg

These are some ideas to get you started. Hope something helps.
Last edit: 3 months 4 days ago by Blue-1.

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3 months 4 days ago - 3 months 4 days ago #5984 by Wobbly
Replied by Wobbly on topic ‘76 R90S. Electrical issues.

mikethebike wrote: I’ve just repaired the brake master cylinder as it lost all its fluid, I don’t know how long this had been an issue, but it was long enough to attack the paint of the main top tube of the frame.

Wobbly wrote: The Starter Relay physically sits just below the Brake M/C. Anytime brake fluid leaks from the reservoir on the under-tank m/c Airhead models, the relay takes a bath in a caustic liquid that is harmful to the relay connections AND the contacts inside the relay. A very serious look at the relay connections and functions is probably in order.


If this bike IS a /7 as Blue-1 indicated, then the problem for Starter Relays is even worse. The /6 starter relay is a metal can with contact on the bottom. When it starts "raining brake fluid", the contacts are somewhat sheltered. But on /7 bikes they went with the "mini-cube" type relay. Those contacts face upward, which makes the caustic brake fluid puddle on the Start Relay contacts.

:ohmy:

Don't hide 'em, Ride 'em !!
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Last edit: 3 months 4 days ago by Wobbly.

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3 months 2 days ago #6024 by mikethebike
Replied by mikethebike on topic ‘76 R90S. Electrical issues.
Quick update to thanks those who gave suggestions.
It turns out the Starter relay was fine, I traced the non turnover issue to a faulty clutch switch.
The headlight issue was the relay, Im amazed at the cost of this relay that has one tiny difference in its internal circuitry from something that costs $10 at Napa!
The horn issue, is a bad horn, popped a spare from a /5 in and voila noise.
Thanks again for the help.
M

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3 months 2 days ago #6030 by Wobbly
Replied by Wobbly on topic ‘76 R90S. Electrical issues.
Hope this all means you're back on the road !

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3 months 2 days ago - 3 months 1 day ago #6042 by mikethebike
Replied by mikethebike on topic ‘76 R90S. Electrical issues.
Errrr, not quite yet, this isn't so much of a restoration as getting a bike that what parked for 25 yrs running again.

Two items left to sort out.
1. This bike came with Morris mags but the rear disc didn't use the R100S Brembo Master and brake cylinders. It used Hearst Airheart, parts for which are now extinct. So I've searched fleabay and got the necessary major parts, small parts from Bobs BMW on the way. Major resto on the Master and Slave cyls.

2. And finally ( I hope) I'm waiting for two nipples for the tops of the Dellortos. The bike came with a few spares that the son of the deceased owner had bought, thinking he would ride it. Unfortunately the cables that he bought are the new ones listed in the fiche. My carbs still had the elbows on top. Without a video chat with Mike Cecchini I would still be trying to figure out how to stretch them to get the slides and needles in.
Last edit: 3 months 1 day ago by Wobbly.

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3 months 18 hours ago #6049 by bremoit
Replied by bremoit on topic ‘76 R90S. Electrical issues.
Motobins in UK sells correct length cables for the early Del carbs. Last check, they were in stock.

Sounds like you got the shorter ones to work though. I've seen where the cable sheathing can be trimmed to accommodate the elbow on the early carb tops.

Cheers

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