1976 R75/6 Electrical issues or not...

[larscwaldner]

Just got the bike back together after being flooded and varmitized. Ready to start. Hear a click in the starter relay and thats it. Checked...
battery for voltage
checked starter and solenoid
neutral switch is shorted
clutch lever is pulled in and switch checked
ground is tight
Bad starter relay? Is there a way to check? Looks like it is wired correctly although couldn't find a diagram and the bottom of the relay has no coresponding numbers.

 

[20774]

Welcome to the forum! Nice that you have been bringing the bike back. Can you explain what you mean by checking the battery for voltage? It can read 12.5 or so as a static charge, but what did your meter show at the battery terminals when you hit the starter button? If it still shows 12.5 or so, then the relay didn't actually close. If it showed less than 10 then it suggests the battery is the problem. Most often, it's the battery. How old is it and can you get it load tested?

 

[larscwaldner]

Electrical issues

Thanks for responding. Battery is brand new. I have it on a charger right now. So if I understand correctly...If when I hit the starter button, if the battery still shows 12.5 the relay is the problem, but if the battery voltage drops signifigantly...then it is the battery that is the problem?

 

[20774]

That's the way I would think. If the starter relay doesn't drop the voltage much, that means the contacts are not closing and staying closed. If the battery voltage just collapses, I would think the battery is suspect. But it could be that something further down the line is drawing lots of power. You say the battery is new. The battery before the one in my /7 now was fine to start with but within a couple of months, it wouldn't hold a charge. Took it back to BMW and got a new one...never looked back.

Articles 16-A (the link below) and 16-B on Snowbum's site has troubleshooting for the starter:

https://bmwmotorcycletech.info/boschvaleostarter.htm

 

[69zeff65]

Explanation please?

What does "flooded" and "varmitized" mean? If the bike was under water for any length of time you might be chasing issues for a while, fix one just in time for another issue to pop up. If the wire harness was chewed up by a varmit then you might think about a new wire harness and a good look at the air filter housing.

 

[larscwaldner]

Electrics

What does "flooded" and "varmitized" mean? If the bike was under water for any length of time you might be chasing issues for a while, fix one just in time for another issue to pop up. If the wire harness was chewed up by a varmit then you might think about a new wire harness and a good look at the air filter housing.

The bike was in a flood, and the mice lived in the top and front of the motor. This has all been remedied. Everything has been disassembled, evaluated, tested and replaced... as required. Wiring harness seems to be fine. I am wondering if the wires to the bottom of the starter relay are correctly oriented as I have no voltage to the black wire on the solenoid when the starter switch is pushed. Unfortunately there are no markings/numbers on the bottom of the relay. It may simply be a function of a couple wires to the wrong spades. Does someone have a schematic of which wires are supposed to go to which spades...specific to a 1976 R75/6?

 

[Omega Man]

Starter relay, and or the starter itself, made be a little grumpy after such a “dip”.
You could always try a “bump” start to see where you are at…..iffin you have a nice hill handy.
OM

 

[20774]

Some diagrams.

https://bmwmotorcycletech.info/schematic1975,1976.htm

Also, in the link in my signature line there is a section on wiring diagrams.

 

[larscwaldner]

Electrics

Starter relay, and or the starter itself, made be a little grumpy after such a “dip”.
You could always try a “bump” start to see where you are at…..iffin you have a nice hill handy.
OM

Starter rebuilt and tested. Black wire from relay to solenoid doesn't get 12 v when trying to start. Wonder if relay is wired incorrectly, or just bad. Is there a way to test the relay? I am trying to confirm wires to relay are correct...but the spades are not indentify-able, there are no numbers next to them? I expected to see 30-85-86-87 and D+?

 

[20774]

Yes, a relay could be tested. Having a stock relay would be helpful. It should have lettering or a diagram on the side of it to identify how it works. It should look like this diagram. It appears that putting 12v across 85 and 86 should pull the relay in. Then you should see continuity across 30/51 and 87. So, no 12v there should be continuity; with 12v, there should be continuity.

 

[Omega Man]

I had a feeling that Kurt would find a schematic.

I like to keep in mind that relay’s, for the most part, are how high amperage “draws” are initiated by smaller wires.

OM

 

[ebeeby]

Sometimes a few good "raps" on a relay with a screwdriver handle can wake them up...

 

[larscwaldner]

Electrics

Yes, a relay could be tested. Having a stock relay would be helpful. It should have lettering or a diagram on the side of it to identify how it works. It should look like this diagram. It appears that putting 12v across 85 and 86 should pull the relay in. Then you should see continuity across 30/51 and 87. So, no 12v there should be continuity; with 12v, there should be continuity.

View attachment 87875

Kurt,
The schematic solved the problem...a black and a blue wire got swapped. Re-connected and I have starter rotation. Now I add some fuel to the floatbowls, check the spark and light it up. Thanks for the help!

 

[20774]

At least now we can stop banging our heads against the wall!!