Newbie with electrical headache

[Airbear]

Just a quick update.

Checked and all the circuit board stuff and it was all OK - found that a poor connection on the indicator relay was all that was stopping the indicators from working. Checked all the starting circuit and it looks like the starter relay is not working - managed to get the starter to turn over by shorting a couple of the contacts, so new relay ordered. Lesson learned is that just because all the functions of the right-hand switchgear were dead doesn't actually mean that the fault lies with the right-hand switchgear!

Neutral switch is u/s though and it looks like the bike's assembled around it - how easy are they to remove?

Hullo Daniel. Good to hear of your success with the indicators.
How have you ascertained that the neutral switch is kaput? Did you get the probes of a continuity tester onto the terminals and click the gear lever into and out of neutral with no positive result?

Replacing the neutral switch will almost certainly involve removing the transmission, or at least shifting it aft an inch or so. Not fun, unless it’s time to lube the input splines or check something else in there. It’s best to be absolutely certain before you go in.

Also, it is possible but unlikely that both the starter relay and the neutral switch would be u/s at the same time. If one goes wrong the bike won’t start, and the other can’t then go wrong – if you follow my logic.

The neutral switch, clutch switch (called the ‘starter cut-off switch’ in the wiring diagram), starter button and starter relay are all inter-related, and there is a diode under the connector board in the headlight that is part of the circuit.

My brain has just run out of charge – I’ll be back.

[Deleted User 62]

Just a quick update.

Checked and all the circuit board stuff and it was all OK - found that a poor connection on the indicator relay was all that was stopping the indicators from working. Checked all the starting circuit and it looks like the starter relay is not working - managed to get the starter to turn over by shorting a couple of the contacts, so new relay ordered. Lesson learned is that just because all the functions of the right-hand switchgear were dead doesn't actually mean that the fault lies with the right-hand switchgear!

Neutral switch is u/s though and it looks like the bike's assembled around it - how easy are they to remove?

Hullo Daniel. Good to hear of your success with the indicators.
How have you ascertained that the neutral switch is kaput? Did you get the probes of a continuity tester onto the terminals and click the gear lever into and out of neutral with no positive result?

Replacing the neutral switch will almost certainly involve removing the transmission, or at least shifting it aft an inch or so. Not fun, unless it’s time to lube the input splines or check something else in there. It’s best to be absolutely certain before you go in.

Also, it is possible but unlikely that both the starter relay and the neutral switch would be u/s at the same time. If one goes wrong the bike won’t start, and the other can’t then go wrong – if you follow my logic.

The neutral switch, clutch switch (called the ‘starter cut-off switch’ in the wiring diagram), starter button and starter relay are all inter-related, and there is a diode under the connector board in the headlight that is part of the circuit.

My brain has just run out of charge – I’ll be back.

This is on a '74, right? Another option is to just pull the wires off the neutral switch and connect them together with a strip of metal, and the bike should start. You can also eliminate the switch on the clutch by connecting the wires together under the rubber boot. I've always been in the habit of pulling in the clutch on startup, so I don't miss the switches.

[Airbear]

This is on a '74, right? Another option is to just pull the wires off the neutral switch and connect them together with a strip of metal, and the bike should start. You can also eliminate the switch on the clutch by connecting the wires together under the rubber boot. I've always been in the habit of pulling in the clutch on startup, so I don't miss the switches.

Correct Timo, and a good test. I've also deleted the clutch switch on mine, as well as the need for it to be in neutral to start, since I now have a different sprung-type starter switch on top of the headlight. I like the arrangement.

I've just dived into Autocad and altered the wiring diagram so it shows only the stuff to do with the starter circuit.



I hope this helps. Power will only go to the starter relay when the transmission is in neutral or the clutch is pulled in. Perhaps somebody with an understanding of the function of the diode could chime in - I suspect my attempt would only confuse matters. My brain is still not indicating full charge.

[Deleted User 62]

This is on a '74, right? Another option is to just pull the wires off the neutral switch and connect them together with a strip of metal, and the bike should start. You can also eliminate the switch on the clutch lever by connecting the wires together under the rubber boot. I've always been in the habit of pulling in the clutch on startup, so I don't miss the switches.

Correct Timo, and a good test. I've also deleted the clutch switch on mine, as well as the need for it to be in neutral to start, since I now have a different sprung-type starter switch on top of the headlight. I like the arrangement.

I've just dived into Autocad and altered the wiring diagram so it shows only the stuff to do with the starter circuit.



I hope this helps. Power will only go to the starter relay when the transmission is in neutral or the clutch is pulled in. Perhaps somebody with an understanding of the function of the diode could chime in - I suspect my attempt would only confuse matters. My brain is still not indicating full charge.

I'm no electrical expert, but it looks to me like the diode is there to isolate circuits that share a common ground. It is the little white box with the black arrow, correct? Someone will be along soon to tell me if I'm wrong.

[DanielMc]

I'd foolishly thought the neutral light was just that - a light. Now I look at Charlie's simplified diagram it's apparent that it's part of an ignition interlock thing.

Charlie - I didn't test the neutral switch, but the light came on when I joined the wires together. I'm pretty sure I tried the starter button at this point (with the clutch wires twisted together too), but I'll double check all that again today.

[Airbear]

I'm no electrical expert, but it looks to me like the diode is there to isolate circuits that share a common ground. It is the little white box with the black arrow, correct? Someone will be along soon to tell me if I'm wrong.

You could be right there, Tim - Snowbum puts it this way –

If the bars clutch lever mounted switch was closed by pulling in the clutch, the starter relay could be operated from the starter button, no matter if the transmission was in neutral OR NOT. The diode was there to prevent the neutral lamp from indicating every time the clutch lever switch was activated. These diodes have been known to short circuit. If so, the neutral lamp will light up every time the clutch lever is used. If the diode failed OPEN, the neutral switch will not allow starter operation UNLESS the clutch is pulled in.


Daniel, there is more here about starting problems including diagnosing the starter relay -

http://bmwmotorcycletech.info/startingprobs.htm

[DanielMc]

Thanks for that link Charlie!

I've just got out from under the bike and I can confirm that when the neutral switch wires are joined together the light comes on but the the starter still won't turn. I've joined the clutch wires at the same time and still no joy. Following Snowbum's fault finding I can confirm that there's no clicking coming from the old starter relay (although there's power there) so I'll see what happens when I try the new relay in the circuit.

On rechecking your wiring diagram I figure that the starter motor gets power via the starter relay when the brown/yellow wire gets earthed by the starter button. Armed with this piece of information I decided to short-cut all the neutral/clutch/starter button wiring and just touch the brown/yellow terminal to earth - and nothing happened. Am I correct in thinking that this would suggest that the relay is u/s?

[George Ryals]

"Neutral switch is u/s though and it looks like the bike's assembled around it - how easy are they to remove?"

It depends on your personal definition of "easy". You can drain the trans ( or lay it on it's side ), remove the rear engine mount bolt, remove the spacer that the bolt runs through then remove the switch. You may need to spray some "freeze it" on the spacer to get it out easily. Having a lift helps.

[Airbear]

Thanks for that link Charlie!

I've just got out from under the bike and I can confirm that when the neutral switch wires are joined together the light comes on but the the starter still won't turn. I've joined the clutch wires at the same time and still no joy. Following Snowbum's fault finding I can confirm that there's no clicking coming from the old starter relay (although there's power there) so I'll see what happens when I try the new relay in the circuit.

On rechecking your wiring diagram I figure that the starter motor gets power via the starter relay when the brown/yellow wire gets earthed by the starter button. Armed with this piece of information I decided to short-cut all the neutral/clutch/starter button wiring and just touch the brown/yellow terminal to earth - and nothing happened. Am I correct in thinking that this would suggest that the relay is u/s?

Daniel, I think your logic is correct - provided there is 12V at the green/black wire and the big red wire. The starter button is a little switch triggering a bigger switch (starter relay) which triggers a bloody great switch (starter solenoid).

Snowbum says you can pull the starter relay apart and see what is going on. He notes that even if the starter relay clicks, the contacts may be corroded to the point where no power is sent to the solenoid. You have said previously that you can get the starter to trigger by shorting wires at the starter relay (basically connecting the big red wire to the big black wire), so it is clear that the big red wire has power. So, if the green/black wire also has power it is reasonable to assume that there is a fault in the starter relay. It might be repairable, but I think you said you have ordered another. Perhaps you could pull the original one apart and improve your knowledge. Maybe take some pics and write what you find, to improve ours.

Nice cat, by the way. Does he offer to assist with the wiring like my cat?

ps: Thanks George, for the advice on replacing the neutral switch. Filed away for future reference.

[DanielMc]

I've just checked with the multimeter and there is 12v at the big red wire and also at the green/black wire on the starter relay - result!

I'll happily deconstruct the old relay with pictures - I'm pretty curious to see what goes on in there myself. Hopefully the new relay should be here in a few days so I'll be able to report back on progress then. Must say that with all the help and support from you all I now feel a lot more confident about what I'm doing when it comes to electrics - the more I see of the multi-coloured spaghetti the less scary it becomes. Big thanks to Charlie for not only providing a crystal clear wiring diagram, but also suggesting I should get it laminated - loving the wipe clean surface mate!

Ginger Tom is one of our rescues and answers to Max. Loves sleeping on my bikes in the garage, but is pretty useless as a mechanic's mate - he blames the lack of opposable thumbs. Here he is on a nice Airline I did lots of work on but sold last year to fund my first R90S: