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R75 died for no apparent reason

Guenther said:
Why not test it by just pushing the horn button. :wave

/Guenther
Click to expand...

Well, of course you could do that as well. The goal was to verify power throughout that (green/black) wire's travel. I kinda tend to solve one problem at a time so if the horn didn't blow then it could have been no power to the horn, a dead horn, or no ground in the path from the horn to the button on the handlebar.
 
1074 said:
Well, of course you could do that as well. The goal was to verify power throughout that (green/black) wire's travel. I kinda tend to solve one problem at a time so if the horn didn't blow then it could have been no power to the horn, a dead horn, or no ground in the path from the horn to the button on the handlebar.
Click to expand...

I finally got to the bike last night. Tried kick starting following the procedure presented in posts above, there was no sign of starting. Cannot count this out due to my age and my inability to provide much power on the kick. As my next course of action I will open the headlight shell and look for fuses.
 
Removing headlight benzel

I would greatly appreciate suggestions for safely removing the headlight bezel. I want to look for the evasive fuses?
 
OK. So if the horn doesn't work then you're back to checking the green/black wire for power with the ignition on.
If you have a stock headlight ring you can use a small screwdriver to pry out the bottom of the ring. It should pop right off. If you see a screw at the bottom then it is most likely an R65 ring so just back off on that screw. The original ring is not very firmly mounted and with wear, will loosen up enough so that the whole assembly will pop off when you smack a pot hole. Then of course the lens hits the fender or fender brace and shatters....
Once you get the headlight out of the way, you'll see the two fuse holders on your right clamped in a rubber mount at the 5 o'clock position. On one end of the fuse holders there will be a solid green wire and a solid grey wire. The green wire is powered by the ignition switch. and past the fuse, powers the green/black wires. And as I said, the green/black wires power the horn, coils and both the front and rear brake switches. So if you do not get a 12 volt reading on the green/black wire anywhere past the fuse then clean or replace the fuse.
If the fuse is the culprit and you replace it, turn on the ignition, and check for power to that wire down the line.
 
I guess the R90/6 with the bad kill switch must have been a 75 model. That was the problem with that particular bike.

With the R75/6 that I restored, you really had to be careful when ordering parts as some parts for an early 75 year model where different than the later R75/6. They had a pretty dodgy electrical set up in those early years from no fuses to 2 fuses. On my R50/5 I had the odd occasion when BMW smoke would spiral up out of the headlight, no fuses as I recall, you had to be quick with the key or the ground.
 
cycleman2 said:
On my R50/5 I had the odd occasion when BMW smoke would spiral up out of the headlight, no fuses as I recall, you had to be quick with the key or the ground.
Click to expand...
I don't know if this will work for a replacement for BMW smoke-

lucassmoke.jpg


:eek

OM
 
cycleman2 said:
I guess the R90/6 with the bad kill switch must have been a 75 model. That was the problem with that particular bike.

With the R75/6 that I restored, you really had to be careful when ordering parts as some parts for an early 75 year model where different than the later R75/6. They had a pretty dodgy electrical set up in those early years from no fuses to 2 fuses. On my R50/5 I had the odd occasion when BMW smoke would spiral up out of the headlight, no fuses as I recall, you had to be quick with the key or the ground.
Click to expand...

The /5 and /6 harnesses are very different. 74 /6 is different than 75-76 /6 as well. I see a lot of electrical problems that get bad information because the responder is using a wiring diagram from the wrong year/model bike.
 
After taking my '74 R75/6 on a pre-purchase test ride, I noted the left rear turn signal appeared to be out. I told the PO and he immediately whipped out a screwdriver, took the lens off, and started fussing with the bulb. I heard a little "tick" and then the bike suffered from the exact conditions yours now experiences. Actually...I can't remember if the brake light worked or not. But otherwise identical. We fished around in the headlight and found the blown fuse. He had no extras, so I came back a day or two later and he said he found a loose connection in the tail light, though I wonder if he maybe had just made contact between two points that he shouldn't have when messing with the bulb. Perhaps you did the same? Anyhow...new fuse and bulb and all has worked fine.
 
Removing headlight benzel

1074 said:
OK. So if the horn doesn't work then you're back to checking the green/black wire for power with the ignition on.
If you have a stock headlight ring you can use a small screwdriver to pry out the bottom of the ring. It should pop right off. If you see a screw at the bottom then it is most likely an R65 ring so just back off on that screw. The original ring is not very firmly mounted and with wear, will loosen up enough so that the whole assembly will pop off when you smack a pot hole. Then of course the lens hits the fender or fender brace and shatters....
Once you get the headlight out of the way, you'll see the two fuse holders on your right clamped in a rubber mount at the 5 o'clock position. On one end of the fuse holders there will be a solid green wire and a solid grey wire. The green wire is powered by the ignition switch. and past the fuse, powers the green/black wires. And as I said, the green/black wires power the horn, coils and both the front and rear brake switches. So if you do not get a 12 volt reading on the green/black wire anywhere past the fuse then clean or replace the fuse.
If the fuse is the culprit and you replace it, turn on the ignition, and check for power to that wire down the line.
Click to expand...

I finally removed the headlight bezel. It was held on with a tiny spring hook that attached to a small black rectangle. I finally removed it with a tiny pair of needle-nose pliers in the process breaking the wire. I assume that is was well worth it given that I expected to find the problematic fuse inside the headlight. To my surprise I found nothing that looked like a fuse. I took pictures, but I don't know how to post them on this site.
Now I'll most likely remove the tank and investigate the electrics surrounding the starter.
 
dodge1chevy2 said:
I finally removed the headlight bezel. It was held on with a tiny spring hook that attached to a small black rectangle. I finally removed it with a tiny pair of needle-nose pliers in the process breaking the wire. I assume that is was well worth it given that I expected to find the problematic fuse inside the headlight. To my surprise I found nothing that looked like a fuse. I took pictures, but I don't know how to post them on this site.
Now I'll most likely remove the tank and investigate the electrics surrounding the starter.
Click to expand...

As far as posting pictures, have a look at this thread-

https://forums.bmwmoa.org/showthread.php?72733-How-to-post-on-the-MOA-Forum

Good luck.

OM
 
dodge1chevy2 said:
I finally removed the headlight bezel. It was held on with a tiny spring hook that attached to a small black rectangle. I finally removed it with a tiny pair of needle-nose pliers in the process breaking the wire. I assume that is was well worth it given that I expected to find the problematic fuse inside the headlight. To my surprise I found nothing that looked like a fuse. I took pictures, but I don't know how to post them on this site.
Now I'll most likely remove the tank and investigate the electrics surrounding the starter.
Click to expand...

I don't recall any small black rectangle as a stock part, so a picture would be a great help. Meanwhile, the fuses are in black cylinders that open by twisting one end.
You might want to look at the top of the main switch. look for a green wire that may be coming from between the switch plate and the top of the headlight shell. You should be able to follow it down to the fuse container. There should be a pair of green/black wires coming out of the other end.
Please let us know what you find.
 
As I recall (which may be full of beans), the original fuses - if and when the factory first installed them - were little white cartridge fuses, as I noted previously (post #8). The twist-to-open fuse holders were a common "previous owner upgrade" when either there were no fuses or the factory clips holding them came apart.
oldBMWfuse.jpg
 
Those were the fuses. They were used 72 and onward. They came as stated in the round, black holders on the /5 models. They were exposed at the rear of the connection board from 74 thru 84. Exceptions were the GS, ST and R45/65.
 
OK, maybe I'm fuzzy, it's been a long time... but at least one of my Slash Fives had this...
B0001883.png
 
Nope, never owned a /6. First /5 was a '71, and the second /5 was a '73.
And the fuses in the older one were on the visible side of the board. For certain.
I don't recall the arrangement on my later one.
 
Last edited:
Pauls1150 said:
Nope, never owned a /6. First /5 was a '71, and the second /5 was a '73.
And the fuses in the older one were on the visible side of the board. For certain.
I don't recall the arrangement on my later one.
Click to expand...
The 71s didn't come with fuses so that was probably a mod by the previous owner. The picture of the headlight that you posted indicates a /6 with a normal key switch going through the left side of the headlight shell.
 
Looking back thru an old album, I've confirmed that both bikes ('71 and '73) had the "plunger" key on top.
The previous parts photo is from the MAX on-line fiche, which indicates that the /5 ran from 8/69 thru 7/80, so there were quite likely partial changes as the bikes evolved. We do know that (at least) the battery, alternator, swingarm, and brakes evolved in that period, so it makes sense that other parts of the electrical system evolved too.
Also, both were bought used, privately, from old guys (like I am now! gosh, over 40 years ago!) who were getting out of riding, and both seemed fairly knowledgeable about BMWs in general, so it's possible that one or both had been modified before I got it.
Both were great bikes and got me coast-to-coast a few times with zero actual issues; can't say that about the new stuff!
Really not worth worrying about... Let's get this thread back on track for dodgethatchevy.
 
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