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Topic-icon Wiring for right control switch

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2 months 1 week ago #4574 by AdamW
Wiring for right control switch was created by AdamW
I have a '70 R75 that I am restoring back to rideable condition. The electrical connections in the headlamp shell were a mess comprised of wire nuts, RTV, rust, and auto connections. I've rewired everything in the shell using color codes for the R75/5. All the wire colors coming into the shell were fine except for the wiring for the right control switch. Two of the wires are different from the schematic. I do have the Green-Yellow, Blue-Red, and Blue-Black. However, the other two wires are Brown-Yellow and Blue-Yellow. One should be ground and the other should be the starter. Currently, nothing happens when I hit the starter. battery reads 12.3v. Most of the lights are working. Exception is the Headlamp (parking light works). The horn is also not working. These are verified working prior to 'repair' and the bike had started.
One item to note is that i replaced the ignition board with the Rockypoint ignition upgrade. Seemed simple enough. I tried switching the Brown-Yellow and Blue-yellow but have the same results. Any suggestions?
Thanks
Adam

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2 months 1 week ago #4575 by Wobbly
Replied by Wobbly on topic Wiring for right control switch
The handlebar switch doesn't control the starter directly, it controls a relay... which then in turn controls the starter solenoid... which then controls the starter motor. So you need to locate the starter relay and see if the button completes a circuit to the relay.

A schematic will tell you whether power is applied at the starter relay, and the handlebar switch supplies "ground", thus completing the circuit (which is the wiring I suspect), OR power is applied at the switch and depressing the button sends power to the starter relay. Either way, relays fail all the time; don't make any assumptions. The starter relay on most models is under the tank on the LH side.

If all that is working, then your next point of research is the starter solenoid mounted on the side of the starter motor, which is (realistically speaking) nothing more than a high current relay. All this is easily reached via the top engine cover held in place with 2 screws.

Ultimately, you should see power applied to the low current terminal on the starter solenoid when the starter button is depressed.

Hope this helps.

Don't hide 'em, Ride 'em !!
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2 months 1 week ago #4576 by AdamW
Replied by AdamW on topic Wiring for right control switch
Hi Wobbly
Thanks for the input. I believe the starter relay is original. Shows 9/70 assuming thats the date made and that it was made in W. Germany. Thought I'd test it out.
On the starter relay, I connected a 12v batt. to pins 15 and 31b. Did not hear a click. While that was connected, tested continuity on pins 87 and 30, not tone. My guess is the relay has enough life to start a few times then died.
-Adam

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2 months 1 week ago - 2 months 1 week ago #4577 by Wobbly
Replied by Wobbly on topic Wiring for right control switch

AdamW wrote: On the starter relay, I connected a 12v batt. to pins 15 and 31b. Did not hear a click. While that was connected, tested continuity on pins 87 and 30, not tone. My guess is the relay has enough life to start a few times then died.


Adam -
While that is a good test, a better test might be to acquire a lighted "test probe". While one might believe that you can always hear or feel the relay clicking, but the real test is does it pass power at the appropriate times. This because you might hear the click, but that does not mean that power is able to be conducted through the old contacts. Or the reverse, the relay may be of a super quiet variety and work perfectly good without giving any external indications of its performance.

With the wire clipped to an appropriate aluminum cyl head fin, the probe can then be used to look for the presence of 12V making its way from the battery. Test probes of this type are commonly available at your local auto parts store (LAPS).

Link To Lighted Test Probe

Hope this helps.

Don't hide 'em, Ride 'em !!
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Last edit: 2 months 1 week ago by Wobbly.

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2 months 6 days ago #4590 by 1843
Replied by 1843 on topic Wiring for right control switch
I seldom get on the forums on the airheads.org site, but, was looking around, and was about to edit one of my articles on the site, and saw this thread.

There may be more than one problem. Be advised that on the /5 (ONLY), the starter relay is special. It contains a transistor, and is connected to the alternator voltage regulator. The purpose is to prevent the starter relay from operating once the alternator produces a bit of output. The test described, done with terminals 15 and 31b (assumed with + voltage to 15, - voltage to 31b) will not cause the relay to close, unless the D+ terminal is connected to 31b. I will assume the relay was out of the bike.
That connection tells the transistor to turn on. Tests on the /5 starter relay should be done only with the relay disconnected and removed from the motorcycle. These relays have been known to have a problem when they and/or the battery is cold. There is a modification to the relay innards, not difficult, on my website;
bmwmotorcycletech.info/slash5cricket.htm
As for the wiring at the handlebars, I suspect you have a 1974 switch unit.
There are a number of wiring diagrams on my site for any need you have.
Snowbum

Bob (Snowbum) Fleischer
Lake Tahoe, California, USA
This email address is being protected from spambots. You need JavaScript enabled to view it.
BMWMOTORCYCLETECH.INFO/
bmwmotorcycletech.info/whothehellissnowbum.htm
FleischerElectronicsService.com/business-4-sale.htm
1995 R100RT;

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