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Topic-icon 1978 RS100 troubleshooting dead electrical

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3 months 4 days ago - 3 months 4 days ago #5100 by Wobbly
Replied by Wobbly on topic 1978 RS100 troubleshooting dead electrical

Wursthead wrote: I got power to the [snip] bike but there’s no turning the power off even with the key in the OFF position ??


Your communication is not clear. Are you saying there is power applied to either or both the Gray and Blue wires coming out of the ignition switch, no matter what key position the ignition switch is in ?

If so, you may need a new ignition switch. Test first. Unplug the Blue and Gray wires from the back of the ignition switch. See if power is still applied to the Blue and Gray wires.
• If there is power, then someone has installed a jumper somewhere in the harness to route power around the ignition switch.
• If there is no power on the Blue and Gray wires once they are disconnected, then you simply need a new ignition switch. BMW does not sell these, so you need to call our friend Rick Jones at Motorrad Elektrik.

Hope this helps.

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 3 days ago #5101 by Wursthead
Replied by Wursthead on topic 1978 RS100 troubleshooting dead electrical
thanks again for your time.

I guess what I'm saying or trying to figure out being a bit of a novice with electrical is that this whole thing was really just about hooking up the right wires from the harness to the right areas on the starter relay harness. if I follow the color codes that the schematic says its confusing because colors don't match up an the numbers differ from what the dual 87 says as to the diagram. so i was poking around a bit but was hesitant to go too deep in fear of frying something . I wish i just had a picture of the wires going into the harness and somehow they were labeled whats what

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3 months 2 days ago #5105 by Wursthead
Replied by Wursthead on topic 1978 RS100 troubleshooting dead electrical
i found a simple schematic backed with photographs of the starter relay and horn relay hookups. so according to the diagram all wires are where they are supposed to be. still dead, upon startup . I'm going to go back and check all connections in the harness next.
any other thoughts?

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3 months 1 hour ago - 2 months 4 weeks ago #5137 by Wursthead
Replied by Wursthead on topic 1978 RS100 troubleshooting dead electrical
I took your advice of course and got the starter relay "dual87" like you said. followed the schematic. all seems good. still no power. the only difference i noticed is the schematic calls out a 87 and 87A input where as the relay just calls out 87 and 87. is there a difference?

Also i noticed that in addition to the main power from the positive terminal hookup there is a red power line that is spliced into create a double connect. one end of that line has power the other doesn't . one side branches off to the horn relay the other the starter relay. thought i had it figured but....
Last edit: 2 months 4 weeks ago by Wobbly.

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2 months 4 weeks ago #5139 by Wursthead
Replied by Wursthead on topic 1978 RS100 troubleshooting dead electrical
I did want to say upon testing all the power lines coming into the relay there is power there but when i tested the red wire going to the ignition switch inside the headlight i get no power. actually nothing lights the probe in there when i poke around

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2 months 4 weeks ago - 2 months 4 weeks ago #5140 by Wobbly
Replied by Wobbly on topic 1978 RS100 troubleshooting dead electrical

Wobbly wrote: • The RED wire is "hot" all the time and straight from the battery. When the relay is in place you should have 12V on both RED wires at the relay socket. From the relay socket, that wire usually shows up on the rear of the ignition switch, or possibly on the RED section of the muti-color circuit board inside the headlamp.

If you've got a lighted test probe, connect the clip to a cyl head fin and poke around the RED wires under the tank and in the headlamp trying to make it light up.

A Simplified Schematic


Per the previously supplied schematic, if you have power on both #87 terminals of the starter relay, but none on the heavy gauge Red wire inside the headlamp, then by deduction the Red wire is broken between those 2 points.

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Last edit: 2 months 4 weeks ago by Wobbly.

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