Electrical/Starter problems on 1972 /5

[2wheeljunkie]

My 1972 R75/5 is having issues with electrical and/or starter. For the past few days the battery hasn't been charging properly, or I don't think it was. At first I thought it was the battery, or the connection to the battery, as the first time this happened I found the wires t to the positive post loose and believed that was the problem, as the battery tender is connected there as well. I got bike started with the kicker and thought a good run would charge the battery, at least enough to start it. But, I had to keep using the kicker every time I shut it off.

I left the battery tender on all night and most of today, but when I checked the bike, the charger was still on solid red, indicating no charge, or that it was still charging. I tried the bike and no response at all, not even a click, click, click like before. I tried the kick starter and it almost started, but it died, and I couldn't get it to offer again. So, I thought I may as well take the battery out and go get another one. When I started to remove the leads to the battery, the starter engaged, even though the key was not on. I should add that every time before, when I pushed the key down to start the bike, all 3 indicator lights (green, red, and yellow) would show, and the headlight would beam if I turned it on, so I am quite certain the battery had some power. The bike was still turning over, although quite slowly, and I had to totally remove the battery lead from the post to get the starter to stop. There must be a short somewhere, but electrical is a weak spot for me so not sure where to begin. I am thinking that maybe the wire to the starter may be loose, but that is just a guess. And I am not sure why the starter was trying to start when I wasn't pushing the button and the key wasn't on. I am also guessing that there must be some kind of drain on the battery to, either keep the battery tender trying to bring it to full charge, or the drain is taking most of the battery's power, and maybe it's because I had the charger still connected and charging that kept the 3 lights on.

Any suggestions or advice greatly appreciated.

 

[20774]

To start with, how old is the battery? Have you measured the battery terminal voltages when you hit the starter button? You may need to have the battery load tested.

As for the self start situation, I'm also a bit challenged there. The starter has basically two wires to it...one is power from the battery and also a connection through the starter relay which then allows for the starter to be grounded and for it to crank. My guess is that something might be wrong with the starter relay.

But you should get the battery checked out and eliminate it from the situation.

And there is this older thread about /5s and starters:

https://forums.bmwmoa.org/showthread.php?62507-5-electrical-issue-starter-button

 

[kinterridge]

Something is closing the circuit to the bendix. Your battery cable + goes to the starter motor and a smaller cable to the starter relay, wheich goes to I think ignition switch then to the start button which sends voltage to close circuit on relay to send 12 v to bendix to engage the starter. Perhaps the relay has failed and moving cables has closed that circuit? With ignition off and good battery do a wiggle test at the relay wire harness. Another possible issue could be at your starter where there is a connection between the starter motor stud and the stud for the bendix, loose wire or insulation missing, bendix came loose? Just some thoughts.

 

[2wheeljunkie]

To start with, how old is the battery? Have you measured the battery terminal voltages when you hit the starter button? You may need to have the battery load tested.

As for the self start situation, I'm also a bit challenged there. The starter has basically two wires to it...one is power from the battery and also a connection through the starter relay which then allows for the starter to be grounded and for it to crank. My guess is that something might be wrong with the starter relay.

But you should get the battery checked out and eliminate it from the situation.

And there is this older thread about /5s and starters:

https://forums.bmwmoa.org/showthread.php?62507-5-electrical-issue-starter-button

Not sure the battery age exactly. I bought the bike late fall, 2020 and the previous owner told me the battery was "fairly new". I would guess it is probably 3-4 years old, so it could be the issue, but the other things make me think something else is causing this. I would have done a test on the battery, but my tester was stolen(along with most of my other tools) last Saturday night and I haven't got a new one yet. I have the battery on the charger now, with all other cables disconnected so will know better tomorrow. I read the other thread and it is interesting, but most of it is "Greek" to me as electrical vocabulary completely confuses me. But my brother is an electronics guy and I may get him to translate.

 

[20774]

Well, your bike's starter is basically a load tester. Put a meter across the battery terminals and hit the starter button. If the voltage drops well below 10v, then you have a bad battery. If the voltage doesn't really change, then something else is wrong and you're not getting power to the starter. Usually that's the starter relay or a loose wire somewhere.

 

[2wheeljunkie]

Something is closing the circuit to the bendix. Your battery cable + goes to the starter motor and a smaller cable to the starter relay, wheich goes to I think ignition switch then to the start button which sends voltage to close circuit on relay to send 12 v to bendix to engage the starter. Perhaps the relay has failed and moving cables has closed that circuit? With ignition off and good battery do a wiggle test at the relay wire harness. Another possible issue could be at your starter where there is a connection between the starter motor stud and the stud for the bendix, loose wire or insulation missing, bendix came loose? Just some thoughts.

I will check this out tomorrow. One thing I just remembered was that when I tried the kick starter today, after the time that it almost started, I heard or heard or heard and felt something move/scrape/scratch (can't come up with an exact descriptor) somewhere behind or under the gas tank area. It was almost like something loose was moving when I stepped on the kick starter. Could have been related, not sure but will investigate further tomorrow.

 

[daz]

Load test your battery!
It costs nothing. You may have more than one problem.

 

[gregfeeler]

I will check this out tomorrow. One thing I just remembered was that when I tried the kick starter today, after the time that it almost started, I heard or heard or heard and felt something move/scrape/scratch (can't come up with an exact descriptor) somewhere behind or under the gas tank area. It was almost like something loose was moving when I stepped on the kick starter. Could have been related, not sure but will investigate further tomorrow.

As others have said, check your battery, but you shouldn't be hearing scraping sounds from under the tank at any time. I'd pull the tank, check all the wiring around the starter, then take it off and take it apart. I think you have a problem there.

 

[2wheeljunkie]

As others have said, check your battery, but you shouldn't be hearing scraping sounds from under the tank at any time. I'd pull the tank, check all the wiring around the starter, then take it off and take it apart. I think you have a problem there.

I am not sure "scraping" is the correct descriptor for what I heard, or possibly thought I heard. I just thought something sounded different.....but then again.... the bike trying to turn over, with the key off and nobody pushing the starter button was very different. I checked the battery with a voltmeter and it is showing 12.5 V, not connected to anything. I put it back on the battery tender, but it still has a red light, indicating it is still charging. I think that the tender is probably not working correctly and I will get another one. I don't want to spend $100.00+ for another battery until I can definitely say this one is not good.

I took everything off the bike to access the starter and the other electrical components and inspected all the wiring and terminal connections. The starter is rusty, but no more so than pictures I have seen of others. I didn't see any corrosion or frayed or bad wires or cables, other than on the 2 coils which had quite rusty clips where the wires plugged in. I sprayed some rust inhibitor on them to see if I could clean them up tomorrow.

As I said, electrical and electronic things are something that I don't know a lot about, but I will check continuity on what wiring I can, put it all back together and see if anything has changed. Only thing I didn't check was the starter switch...didn't want to take it apart if I didn't have to. It could be the relay as I had been getting some of the cricketing when I went to start the bike. I have read Snowbums solution to this and it is beyond my skillset, but I believe my brother could do it. I just don't want to do it if that is not the problem.

Thanks to all replies, I know with everyone's help and some trial and error that I will find the solution....luckily riding season is just about over here in Canada, so I have all winter to get it running again.

 

[Omega Man]

You may want to try the kick starter with the batter tender connected and as many accessories/lights off as possible.
OM

 

[2wheeljunkie]

You may want to try the kick starter with the batter tender connected and as many accessories/lights off as possible.
OM

I won't be able to do that until I get things back together ,but when I tried this before, I didn't get any response.
I never have any accessories on, and the only one I have is the headlight which I haven't had turned on since this problem started. I don't have a load tester, but I read on line about how to do this with a multimeter, so I will try that once I get things back together. That won't be until Wed of next week at the earliest, as I am too busy the next few days.

Keep the info coming, I am a newbie to working on this bike....back in '72 when I had my first /5, I never had to do more than put gas in it, change the oil, and scrape the frost off the seat when going and returning from work....those were the days!

 

[Omega Man]

You could also parallel a known good battery and try the kick start- like jumping a car.
OM

 

[daz]

Here most auto supply stores will load test a battery for free. To check if your charger is working measure your voltage with the charger plugged in and not plugged in. But the battery must be disconnected to do this.

 

[ebeeby]

Here most auto supply stores will load test a battery for free. To check if your charger is working measure your voltage with the charger plugged in and not plugged in. But the battery must be disconnected to do this.

Yes, this must be the first step. A bad battery with a shorted cell can show 12v on a VOM. Forget everything else until you get this done.

 

[2wheeljunkie]

Yes, this must be the first step. A bad battery with a shorted cell can show 12v on a VOM. Forget everything else until you get this done.

I haven't had time to do much with the bike, but Sat night when I checked the battery with the multi meter(battery is out of the bike, sitting on the lift), and the voltage was 12.5. I left the charger on all night and Sunday am it was still on red, so I disconnected the charger, put the meter on it. and it only registered 0.7 V. The battery is definitely dead and done. I have a new one on order and it will be here in a few days. I won't be able to work on the bike until next week anyway, so I decided to get it from the cheapest place, $50-60 cheaper than any local store. I don't know if there are any further electrical problems or not, quite possibly not...I should have listened to everyone who said it was probably the battery...hopefully that's all. Will let you know end of next week.

 

[kinterridge]

From your 1st post:
"When I started to remove the leads to the battery, the starter engaged, even though the key was not on. I should add that every time before, when I pushed the key down to start the bike, all 3 indicator lights (green, red, and yellow) would show, and the headlight would beam if I turned it on, so I am quite certain the battery had some power. The bike was still turning over, although quite slowly, and I had to totally remove the battery lead from the post to get the starter to stop."

Glad you determined your battery is an issue, but were you able to determine the self starter engagement you mentioned as well with the ignition off?

 

[2wheeljunkie]

From your 1st post:
"When I started to remove the leads to the battery, the starter engaged, even though the key was not on. I should add that every time before, when I pushed the key down to start the bike, all 3 indicator lights (green, red, and yellow) would show, and the headlight would beam if I turned it on, so I am quite certain the battery had some power. The bike was still turning over, although quite slowly, and I had to totally remove the battery lead from the post to get the starter to stop."

Glad you determined your battery is an issue, but were you able to determine the self starter engagement you mentioned as well with the ignition off?

I haven't been able to do that, as I haven't been able to start, or attempt to start, the bike. I looked at all the connections around the starter, the coils, and the battery leads and didn't see any corrosion or frayed wires, or nothing that would short out. It could possibly be something in the headlight housing where the key inserts, or it could be something in the switch button. I will wait until I get the battery before I do any more digging. Thanks for the reminder. I am going to see if I can get time to put the bike back together this week, and while I am at it I have to put a new rubber seal around the ignition points protector area. I should know more by next week sometime.

 

[James.A]

The starter relay, under the tank on the left side of the frame backbone, is the electrical gate keeper on a /5, provided it is the original relay. Everything needed to engage the starter happens in that component. It also has a feature to dis-able the electric start if the motor is running. This anti-restart feature can also dis-able the starter function if the alternator rotor goes open. There is a lot going on inside the thing. Maybe check and clean up all the connections on it.

 

[2wheeljunkie]

The starter relay, under the tank on the left side of the frame backbone, is the electrical gate keeper on a /5, provided it is the original relay. Everything needed to engage the starter happens in that component. It also has a feature to dis-able the electric start if the motor is running. This anti-restart feature can also dis-able the starter function if the alternator rotor goes open. There is a lot going on inside the thing. Maybe check and clean up all the connections on it.

I will double check that as I looked at it and didn't see anything obvious, but will check again while the bike is apart. I have read on Snowbum's site about the transistor in the starter relay that can cause problems usually in cold temps or low battery issues. I am not sure if it is an original relay or not, but will get some numbers off it and see what I can find out.

 

[daz]

It is a good policy to put your brand new battery on the charger when you get it. Make sure it is fully charged.