74 R75/6 electrical woes

[sap06003]

Hi guys! Looking for some help with my 1974 r75/6, it runs pretty well but i am experiencing a few electrical problems.

Through my exploration i have found:

My ignition switch only seems to have 4 positions, it is an oe bmw with a factory style key, I don't think they made a 4 position though, this key also will not lock the seat, does this mean it was swapped from another model? When i check wiring diagrams, it also shows the two center spades connected to a red wire, only one spade is connected to the red wire, should there be a jumper?

The left switch on the bars looks new, and according to my research this is a hard to find one bike part, to turn the headlights on, you must hold down the left switch. I am assuming this is the wrong switch for the 74. Does anyone know how to tell if the switch is correct?

I got this bike in "it ran when it was parked in the bar 15yrs ago" condition, so it may have been parked for these issues, I am assuming it was not correct.

Thanks!
Sean

[barryh]

Depends on whether you count the off position but you might have the euro ignition switch. This is a poor quality diagram and it's for a later model but it shows the difference between the US and Euro switches.

Ignition switch.JPG (14.36 KiB) Viewed 1681 times

[Rob Frankham]

The first point is that Model year '74 /6 machines are quite different electrically to model year '75 and '76 so you have to be very careful which wiring diagram you are referring to.

I've looked through a number of /6 wiring diagrams and Clymer (the old pre Haynes Clymer that is) shows a four position switch on the 1974 /6. However, the diagram is very bad and the position/wiring information doesn't appear to make sense. For what it's worth, it only shows one red wire to the switch. Hopefully, someone out there will have a reliable /6 US wiring diagram and will chip in.

That being said, if everything works as it should, why worry about it.

As far as the key goes, the two locks would have matched when the bike left the factory (along with the steering lock and fuel cap lock (if fitted). If they don't match now, it simply means that either a lock is defective or it has been swapped perobably woth another compatible lock. A good locksmith should be able to make a compatible key if the locking seat is important to you.

Hope you get a definitive answer.

Rob

[sap06003]

Thanks rob, the problem i am having is that the headlights only work when holding down the left switch(pushing it like a button). I should go through and verify the exact conditions when the lights work and don't work. I will try to get together some more clear info/diag this weekend, i really don't want another summer to get away from me with this thing!

Ill post some pics once she isnt covered in dust

[Rob Frankham]

On the face of it, the headlamp circuit would appear to be not working at all. Pushing down the left switch (dip switch) engages the headlight flash circuit which uses a completely different current path to the normal headlamp circuit ( '74 models don't have the lighting relay fitted to '75 models and later).

In essence, the headlight circuit works like this... the yellow/white wire on the igniton switch takes current to the handlebar switch gear when the switch is in the 'headlights' position. At the switchgear, the current is passed to the dipped beam filament (yellow wire) or Main Beam (White wire).

The flasher circuit takes current from the green wire on the ignition switch whenever the switch is in an 'on' position (i.e. not off or parking) and passes it to the handlebar switchgear so that, when the flasher is pressed, the current is passed to the main beam filament.

In your case, since the flasher works but neither main or dipped beam work, it's a pretty fair bet that the headlight bulb earthing is OK. (otherwise the flasher wouldn't work) and a reasonable assumption that the wiring between the handlebar switch and the bulb is OK (otherwise one or the other would probably work... the alternative is that both yellow and white wires are defective).

Given this, as a first port of call, I would be concentrating on the yellow/white wire from the ignition switch to the handlebar switchgear... one other possibility comes to mind. If the ignition switch is actually a five position switch and the fifth position is, for some reason, not working (bearing in mind that you describe it as a four position switch, this would also cause the symptoms you are experiencing.

Of course, this assumes that your bike is indeed a '74 model with the older electrical arrangement (the later /6s are very different in this area) and that the flasher circuit works while neither the main beam or dip beam circuits are working.

Hope you get to the bottom of it quickly...

Rob

[sap06003]

Rob, Thanks for taking the time to write that out! It was the white/yellow wire, the terminal showed power when it should, so i pull on the connector and the wire pulled right out, crimped a new connector on and all set! I have to do a thorough test of the ignition switch positions tho, it still only has 4 positions with the headlights working in "4" only

[Rob Frankham]

Glad you found the problem... makes perfect electrical sense...

I'm interested in the 4 position switch, what do the four positions do?

For example, a five position switch would be:-

0) Off
1) Park
2) Igniton only
3) Ignition and side lights (Position lights)
4) Ignition and headlamps (sometimes side lights as well)

Am I right to suspect that position 2 is ignition/sidelights and there is no position that gives Ignition on it's own?.. that would make sense in some jurisdictions.

[sap06003]

Rob,
Sorry for the delayed reponse, life is quite hectic these days. On the subject of the 4 positions, what does a park position mean? what should have power? At this point all i know is she starts in 3 and 4 and 4 has headlights.

So, I've got her running pretty well, first thing i did was pretty obvious fix, the wires under the front cover were in pretty bad shape and the sparks on the points/advance unit seemed to be "jumping around" so i replaced what wires i easily could and put new spade connectors on the ones that were harder to replace. No jumping sparks. Next i cleaned the carbs, which were brand new when installed, i found a small piece of metal sitting on top of one of the main jets! Fired right up and ran pretty well after that. Getting into the timing tonight and then hopefully a test ride!

[Rob Frankham]

IN the 'park' position there should be power to the sidelight (parking light... whatever you call the small bulb in the headlamp shell where you are), the tail light and the instrument lights, but no power to engine, headlights or other electrics. It's literally for leaving the bike parked with illumination.

Rob

[SteveD]

... Next i cleaned the carbs, which were brand new when installed, i found a small piece of metal sitting on top of one of the main jets! Fired right up and ran pretty well after that.

I'm wondering where that piece of metal has come from? Reinstalling the atomiser needs to be done to avoid cracking the intake bore. It might be worth taking a look there. Though, I can't see how a small metal part from there would relocate itself to above the MJ?

2. bing throat.jpg (83.37 KiB) Viewed 1057 times