Hi there - I recently got my '71 R60/5 back on the road again after 4 years in storage. During the first ride yesterday at around 40mph the red charge light came on in the headlamp assembly and I began to lose power. When I pulled over to the side of the road the engine stopped and all lights went out. I figured it must be a faulty alternator/rotor as the battery is new and didn't think it was a short in the system because of the way the charge light came on and loss of power when I was riding. The starter wouldn't work and no indicator lights appeared with the key fully inserted - but I was able to get it started using the kick starter, and drive it with limited power at my disposal. I had no lights (turn signal, headlamp, indicators, etc.) on my way home, but when I got home and parked it in the driveway strangely everything started working again perfectly. It worked fine today for a quick 3 mile ride around the neighborhood but I obviously don't want to chance taking it for a longer ride until I get this sorted. If anyone else has experienced something similar please let me know, I figure I will need to test/replace the rotor/stator, diode board, and v regulator, but if I'm missing something more simple/obvious I'd appreciate any advice you can offer. Thanks so much.
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R60/5 '71 - Loss of power red charge light illuminated at 40mph
- Thread starter leighland
- Start date
Welcome to the forum! Certainly do some testing before you start throwing money at it. New battery, but I would consider verifying that it is good. Note that the bike should run "OK" without an alternator system. Basically, the bike runs off the battery and the alternator just keeps "filling it up" of what's been drained. If the alternator fails on the open road, one can fashion a system to keep putting a new charged battery back in the system (or strapped to the back seat) and get further down the road.
Be sure that the battery ground at the back of the transmission is clean and tight...don't ham fist the bolt holding it in, but make sure it's not loose.
I'd test the battery first by putting your voltmeter across the terminals and use the electric start...what does the reading start at and then while you're cranking it. If the battery is bad, the voltage will be south of 9v. If you get past that, there are steps to testing the alternator. Snowbum has some stuff here:
https://bmwmotorcycletech.info/trbleshootALT.htm
Rick at Motorrad Elektrik also sells a book that breaks the testing down even better:
http://www.motoelekt.com/goodstuff.htm
Let us know how you make out.
Be sure that the battery ground at the back of the transmission is clean and tight...don't ham fist the bolt holding it in, but make sure it's not loose.
I'd test the battery first by putting your voltmeter across the terminals and use the electric start...what does the reading start at and then while you're cranking it. If the battery is bad, the voltage will be south of 9v. If you get past that, there are steps to testing the alternator. Snowbum has some stuff here:
https://bmwmotorcycletech.info/trbleshootALT.htm
Rick at Motorrad Elektrik also sells a book that breaks the testing down even better:
http://www.motoelekt.com/goodstuff.htm
Let us know how you make out.
stevenrankin
Active member
Perhaps
I don't have much knowledge of this bike.
I had a brother in law who had one and he had all kinds of similar problems with the ignition key/switch system used on the bike. From what he told me they can be fussy and if they sit, they may not work properly.
His problem turned out to be a bad connection in the switch itself. I can't say how he repaired it because he did not do the repair himself a local shop did it for him.
I am sorry I cannot add more information. Good luck, St.
I don't have much knowledge of this bike.
I had a brother in law who had one and he had all kinds of similar problems with the ignition key/switch system used on the bike. From what he told me they can be fussy and if they sit, they may not work properly.
His problem turned out to be a bad connection in the switch itself. I can't say how he repaired it because he did not do the repair himself a local shop did it for him.
I am sorry I cannot add more information. Good luck, St.
Steven -
It's really not that much different...OK, the ignition switch setup is different and consists of a PC board with soldered wires in the top part of the headlight shell. But the big functions work just the same way. As I said, the bike should run without and alternator as long as the battery and its connections are solid.
It's really not that much different...OK, the ignition switch setup is different and consists of a PC board with soldered wires in the top part of the headlight shell. But the big functions work just the same way. As I said, the bike should run without and alternator as long as the battery and its connections are solid.
Thanks so much for the quick reply! I tested the battery and it’s reading 14.17 before cranking and 13.25 while cranking/running. I also verified the connection from the lead to the back of the transmission is clean and secure. So I guess what I need to do is begin to test the other components and I’ll have a look at the websites you provided. In terms of the switch, I replaced most of the wiring in the headlight along with the wiring harness previously and I haven’t had an electrical issue since that time - and again I don’t think it has anything to do with the switch/wiring because of the way this happened - riding along at 40mph and then losing power with the red charging light coming on. It wasn’t a situation of everything being dead (at first at least) - but who knows 
thanks again for the valuable feedback - I appreciate it. david
thanks again for the valuable feedback - I appreciate it. david
Thanks for your reply - no I didn’t take the front cover off after getting it out. But I’ll make certain to disconnect the cable before doing so when I troubleshoot the rotor and diode board.
m_stock10506
Well-known member
If you don’t have a voltmeter on the bike, connect one to the battery and watch it for any sudden change.
I had an AGM battery a while back that had an intermittent open in the plates. It would go to zero volts. As soon as I slowed the rpm for a turn the alternator couldn’t produce enough current to keep the motor running. I would check it later and the battery had full voltage and started the bike. Wasn’t until I stuck a voltmeter on the handlebars and rode around the neighborhood that I saw the drop to zero and the bike died. Had to push it two blocks home. New battery fixed it up.
Just because you put in a new battery doesn’t mean it is good.
I had an AGM battery a while back that had an intermittent open in the plates. It would go to zero volts. As soon as I slowed the rpm for a turn the alternator couldn’t produce enough current to keep the motor running. I would check it later and the battery had full voltage and started the bike. Wasn’t until I stuck a voltmeter on the handlebars and rode around the neighborhood that I saw the drop to zero and the bike died. Had to push it two blocks home. New battery fixed it up.
Just because you put in a new battery doesn’t mean it is good.
It’s an early ‘71 so no fuses sadly...amusingly enough this is why I needed to replace most of the wiring in the headlamp shell after a somewhat catastrophic short and melt-down of the wires (minor headlamp fire really) .. I should have installed fuses back then when it happened.
That’s a great idea - thanks so much. I’ll rig something up and go for a ride with it taped to my handlebars this afternoon.
stevenrankin
Active member
Another melt down
I know another fellow who had a melt down fire in his head light due to a loose connection in there. It happened on a group trip he was taking.
Not to nag but check the connections and such on the switch and in the headlight. As I mentioned my brother in law had very similar symptoms with his same bike, it was the switch or something to do with the switch. The fellow with the fire in his headlight had a wire come off in the shell shorting out.
Loose wires will do weird things and sometimes bad things. St.
I know another fellow who had a melt down fire in his head light due to a loose connection in there. It happened on a group trip he was taking.
Not to nag but check the connections and such on the switch and in the headlight. As I mentioned my brother in law had very similar symptoms with his same bike, it was the switch or something to do with the switch. The fellow with the fire in his headlight had a wire come off in the shell shorting out.
Loose wires will do weird things and sometimes bad things. St.
Thanks Steven - I appreciate your persistence and will follow your advice and check over all the connections again in the headlamp just to rule that out...much simpler than pulling out the rotor etc. To be honest the more I think it through, the more I suspect it’s either a short or the battery is faulty (even though its reading fine when I have the bike running on the center stand).
As Kurt mentioned earlier the alternator simply supplies the battery with power and the bike should run without it. I’m still perplexed however by the way this all happened. Why would the red light come on at 40mph with rpms around 4000? I believe the light is governed by the alternator and goes off when the engine produces enough power to charge the battery - so my initial assumption was that the problem was related to the alternator...Sooo strange. Thanks again for your feedback. David
and will follow your advice and check over all the connections again in the headlamp just to rule that out...much simpler than pulling out the rotor etc. To be honest the more I think it through, the more I suspect it’s either a short or the battery is faulty (even though its reading fine when I have the bike running on the center stand).As Kurt mentioned earlier the alternator simply supplies the battery with power and the bike should run without it. I’m still perplexed however by the way this all happened. Why would the red light come on at 40mph with rpms around 4000? I believe the light is governed by the alternator and goes off when the engine produces enough power to charge the battery - so my initial assumption was that the problem was related to the alternator...Sooo strange. Thanks again for your feedback. David
stevenrankin
Active member
Kurt is correct
Kurt is correct, in some ways, In the old days before computers a fast way to test the charging system of a car was to pull the negative terminal off the battery while the car was running. If the car kept running, the charging system was "working" albeit maybe not properly but enough to keep the car running. If the car died, then we knew it was running on only the battery and the charging system was bad.
Very simple like the BMW charging system. The battery is for starting one the bike is running and engine RPM is above a certain point, the battery is no longer needed in the system except to give a needed charge to the alternator to energize it so it can produce a charging current. Unlike a generator, an alternator needs a bit of a current from the battery to energize it to allow it to produce the charge to run things and top off the charge on the battery. Whew, mind you I am not an engineer nor a teacher so I am struggling to describe how this works.
In a properly working system, the battery provides the voltage and current to run the starter. At idle, when the red light comes on, the bike is in fact running still off the voltage in the battery. When the RPM gets above a certain point, the charge from the alternator is sufficient to take over, top off the battery to full charge an power the ignition, lights and such. At this Point except for giving a bit of a current flow to energize the alternator the battery is going along for a ride. Of course at idle again, the current produced by the alternator drops to the point where the battery has to take over the job again. This is repeated all the time we are riding. As long as we are moving and above a certain engine RPM the system will run the ignition lights and charge the battery. If the red light is on more than off, there is a possibility the battery will get depleted to the point where it will die. Now, the voltage required (or should I say energy?) to run the bike' ignition is very minimal. Most of the charge produced by the alternator is used for headlight and such.
So, I bike will run a long time on a system in which the alternator has quit charging as long as the lights are turned off. (I am on another track, sorry). At this point, the starter most likely will not turn the bike over at all, and after a long enough period, the bike will just plain quit as there is not enough charge in the battery to charge the ignition coils.
I think of the charging system like a water system. Where does the water flow from up to down, high pressure too low. In the charging system is a diode. This little bugger blocks charge from going in a certain direction, bear with me, I am struggling to describe this. It's job is to prevent the red generator light from being illuminated. (If current flowed heater skelter, the light would be on all the time). When in proper charging mode, at an RPM where the alternator is spinning enough to produce full charge, the diode blocks any current flow through the red light. So, the light stays out. I don't want to say the current is flowing one way but that is the only way I can describe it for now. When the alternator charge drops below a certain voltage/charge, the current flow is changed and the energy comes then form the battery. The diode allows current flow in this direction and the light is illuminated. You are running off the battery now. In either situation, the light bulb needs to be in the circuit to complete it so the system can work properly. That is one of the weakness of the BMW airhead charging system. A blown bulb means no charge.
So all this nonsense I have written does not mean a thing if there is a loose wire or connection on any of the components in the system. You could have a red light come on at any time just because a wire is shorting the bulb wire, giving it a jolt of juice. the light may come on because there is a wire off somewhere and the charge balance is on the battery side of the scale.
Given my vastly limited knowledge of the model of bike you have and the two incidents I have heard of, leads me to investigate the headlight shell area and switch. I am NOT saying there can't be anything wrong with the charging system. Just trouble shoot calmly and start with the simple thing first.
IF all the connections are tight and you have a red light at 4000RPM, there is a good chance there is in fact something wrong with the charging system. As for the bike cutting out, I really believe it is a loose connection causing that problem. In a very bad scenario, a dead short in a bad battery could drain the system while running to zero and cause the bike to quit. remember, the alternator needs a charge from the battery to energize and the battery needs to have voltage to energize the coils. I must admit, I have seen this happen in the case of cheap poorly made batteries it is not as rare a thing as it should be.
So, I have written like a nut, and perhaps will look like a fool, some of the other learned members of the forum will of course fill in the gaps I have left or correct me. I hope you can use what I say and solve your problem. Cheers, St.
Kurt is correct, in some ways, In the old days before computers a fast way to test the charging system of a car was to pull the negative terminal off the battery while the car was running. If the car kept running, the charging system was "working" albeit maybe not properly but enough to keep the car running. If the car died, then we knew it was running on only the battery and the charging system was bad.
Very simple like the BMW charging system. The battery is for starting one the bike is running and engine RPM is above a certain point, the battery is no longer needed in the system except to give a needed charge to the alternator to energize it so it can produce a charging current. Unlike a generator, an alternator needs a bit of a current from the battery to energize it to allow it to produce the charge to run things and top off the charge on the battery. Whew, mind you I am not an engineer nor a teacher so I am struggling to describe how this works.
In a properly working system, the battery provides the voltage and current to run the starter. At idle, when the red light comes on, the bike is in fact running still off the voltage in the battery. When the RPM gets above a certain point, the charge from the alternator is sufficient to take over, top off the battery to full charge an power the ignition, lights and such. At this Point except for giving a bit of a current flow to energize the alternator the battery is going along for a ride. Of course at idle again, the current produced by the alternator drops to the point where the battery has to take over the job again. This is repeated all the time we are riding. As long as we are moving and above a certain engine RPM the system will run the ignition lights and charge the battery. If the red light is on more than off, there is a possibility the battery will get depleted to the point where it will die. Now, the voltage required (or should I say energy?) to run the bike' ignition is very minimal. Most of the charge produced by the alternator is used for headlight and such.
So, I bike will run a long time on a system in which the alternator has quit charging as long as the lights are turned off. (I am on another track, sorry). At this point, the starter most likely will not turn the bike over at all, and after a long enough period, the bike will just plain quit as there is not enough charge in the battery to charge the ignition coils.
I think of the charging system like a water system. Where does the water flow from up to down, high pressure too low. In the charging system is a diode. This little bugger blocks charge from going in a certain direction, bear with me, I am struggling to describe this. It's job is to prevent the red generator light from being illuminated. (If current flowed heater skelter, the light would be on all the time). When in proper charging mode, at an RPM where the alternator is spinning enough to produce full charge, the diode blocks any current flow through the red light. So, the light stays out. I don't want to say the current is flowing one way but that is the only way I can describe it for now. When the alternator charge drops below a certain voltage/charge, the current flow is changed and the energy comes then form the battery. The diode allows current flow in this direction and the light is illuminated. You are running off the battery now. In either situation, the light bulb needs to be in the circuit to complete it so the system can work properly. That is one of the weakness of the BMW airhead charging system. A blown bulb means no charge.
So all this nonsense I have written does not mean a thing if there is a loose wire or connection on any of the components in the system. You could have a red light come on at any time just because a wire is shorting the bulb wire, giving it a jolt of juice. the light may come on because there is a wire off somewhere and the charge balance is on the battery side of the scale.
Given my vastly limited knowledge of the model of bike you have and the two incidents I have heard of, leads me to investigate the headlight shell area and switch. I am NOT saying there can't be anything wrong with the charging system. Just trouble shoot calmly and start with the simple thing first.
IF all the connections are tight and you have a red light at 4000RPM, there is a good chance there is in fact something wrong with the charging system. As for the bike cutting out, I really believe it is a loose connection causing that problem. In a very bad scenario, a dead short in a bad battery could drain the system while running to zero and cause the bike to quit. remember, the alternator needs a charge from the battery to energize and the battery needs to have voltage to energize the coils. I must admit, I have seen this happen in the case of cheap poorly made batteries it is not as rare a thing as it should be.
So, I have written like a nut, and perhaps will look like a fool, some of the other learned members of the forum will of course fill in the gaps I have left or correct me. I hope you can use what I say and solve your problem. Cheers, St.
Wow - thank you so much Steven for taking the time to share all of this valuable information - I am really deeply appreciative. Your explanations are easy to understand and incredibly helpful to me as I try and sort out this issue.
I will begin by testing the voltage produced during a ride as was suggested earlier, looking for large variations. If this proves not to be an issue I will then carefully look through all of the wiring in the headlamp checking for shorts before embarking on testing the charging system. I'll post my findings when I get this sorted out, and hopefully this thread will be of use to someone else, who may find themselves in a similar situation. Once again many thanks - cheers, david
I will begin by testing the voltage produced during a ride as was suggested earlier, looking for large variations. If this proves not to be an issue I will then carefully look through all of the wiring in the headlamp checking for shorts before embarking on testing the charging system. I'll post my findings when I get this sorted out, and hopefully this thread will be of use to someone else, who may find themselves in a similar situation. Once again many thanks - cheers, david
The light comes on when there is current flow through the bulb element. If the voltage on either side of the bulb - one representing the alternator output and the other side being the battery voltage - are essentially the same, no current flows and the bulb is dark. But when a voltage differential shows up, then the bulb lights. So one side or the other wasn't working right. Often times you'll hear people talk about a dimly glowing light and this indicates just a small voltage difference...could be a number of things such as bad grounds, etc. I don't know enough to specify when the bulb is bright...is that 1v or 5v difference...not sure.
Intermittent electrical problems are a bear to work on. Until you can make it do it on command, and it doesn't burn you down in the process, you're going to have to keep checking the pieces out until you have found an actionable item.
Steven -
I'm not too sure about the battery not being needed on our bikes once the engine has started and the alternator is working. The bikes are a battery-coil ignition and I believe the battery is important in this context. I haven't experimented, but I wonder if the bike will truly run if the battery ground is disconnected. I agree that was the case with older car engines. I have my doubts on the bike, but I'm not willing to trying to prove me wrong! I'm ready to be corrected!
I'm not too sure about the battery not being needed on our bikes once the engine has started and the alternator is working. The bikes are a battery-coil ignition and I believe the battery is important in this context. I haven't experimented, but I wonder if the bike will truly run if the battery ground is disconnected. I agree that was the case with older car engines. I have my doubts on the bike, but I'm not willing to trying to prove me wrong! I'm ready to be corrected!
Older cars had generators, not alternators. You might want to check the consequences of disconnecting the battery from the charging system while it’s running. If I did that on my boat, I’m looking at a new alternator (the diodes will be fried). I don’t know if these systems are different.
