Newbie with electrical headache

[DanielMc]

Firstly hello to all - I'm new here and this is my first post, though I notice a few familar names from other BMW fora.

I've just bought another airhead - a 1974 R90S, but unlike my other bikes (a 1976 R90S and a 1980 R65LS) this new one doesn't run.

I bought it as a nearly completed restoration but the previous owner lost enthusiasm when he couldn't get the wiring to carry the appropriate amount of smoke on reassembly. The symptoms are that when the key's turned there's no alternator or neutral light (but there is an oil light) and the indicators and start button are inoperative (whole rh switchgear). No brakelights either, but the ignition switch turns on all lights (pilot, instruments and main) as appropriate, lh switchgear works and the voltmeter reads 12V when the oil light comes on.

Previous owner reckoned he misplaced something on the circuit board, and I'm already indebted to Airbear for his excellent wiring diagram but the back of my headlight bucket looks like a snakes wedding and I was hoping there might be an easy explanation for the hard-of-thinking before I venture in there with a multimeter. Should point out that this bike carries the /5 type switches.

[Ken in Oklahoma]

Firstly hello to all - I'm new here and this is my first post, though I notice a few familar names from other BMW fora.

I've just bought another airhead - a 1974 R90S, but unlike my other bikes (a 1976 R90S and a 1980 R65LS) this new one doesn't run.

I bought it as a nearly completed restoration but the previous owner lost enthusiasm when he couldn't get the wiring to carry the appropriate amount of smoke on reassembly. The symptoms are that when the key's turned there's no alternator or neutral light (but there is an oil light) and the indicators and start button are inoperative (whole rh switchgear). No brakelights either, but the ignition switch turns on all lights (pilot, instruments and main) as appropriate, lh switchgear works and the voltmeter reads 12V when the oil light comes on.

Previous owner reckoned he misplaced something on the circuit board, and I'm already indebted to Airbear for his excellent wiring diagram but the back of my headlight bucket looks like a snakes wedding and I was hoping there might be an easy explanation for the hard-of-thinking before I venture in there with a multimeter. Should point out that this bike carries the /5 type switches.

Welcome to the forum Daniel.

There are a lot of people here who can help you with your electrical problems. I might be one of them. Your question, however, is hard to get around. I think we could use some more information from you.

First, how conversant with electrical systems are you? For example, can you read and follow a wiring diagram? Do you understand ohm's law, or do you just have a rough idea of what voltage, resistance, current, an power are about? You talked about a multimeter, so I gather that you are pretty familiar with electrical things? The reason I'm asking this is so we can tailor our advice to your capabilities.

Also various people will have different approaches to your problems. Without knowing more about your problems I have one.

First, it strikes me that the previous owner wasn't conversant with wiring. Did he try to use the old wiring harness or did he install a new one? Whichever it was he did it wrong. You talked about the smoke in the wires. Did he actually smoke some wires or were you simply describing his skill level? You will need a good harness to work with, or be prepared to wire around some of the wiring harness problems, or buy a new (expensive) wiring harness. But hey, it's a first year R90S, worth it if needs be!

Since it was a restoration that presumably means that every electrical item was unplugged and then plugged back again. Perhaps, before chasing specific problems you should consider unplugging everything and color coded wiring diagram in hand, plug everything back personally. You listed some items that didn't work, but there may be other things that were wrong. If you were to redo the connections (making sure they are clean and bright) you would be in a better position to start trouble shooting. Plus you could tidy up the rat's nest in the headlight shell. I know that's a daunting proposition considering all that is going on inside the headlight shell and the circuit board, but I think it might be the better approach. In the case of the board inside the headlight shell, you've noticed that it's color coded and the wires are also color coded. Matching color coded wire to the same color coded terminal will get you a long way.

It's understandable that you might not want to fool around with the stuff that does work and would rather work on the stuff that doesn't. Then my procedure would be to tackle one problem at a time. The way I would go about it would be to pick a problem, any problem, and, wiring diagram in hand, trace the current path from positive battery terminal through the function in question and then through frame ground back to the negative battery terminal. Where does the 12 volts get lost (or for that mattere where is it present when it shouldn't be)? Fixing that problem is likely to solve multiple problems.

In your specific case the procedure might be simplified. Some things are working. For example you will be getting 12 volts to the ignition switch. I would make sure by checking that the red wire to the ignition switch always has 12 volts present. When that is verified check the switching positions, one by one, to make sure that, depending on the position of the key, 12 volts is present or not on each terminal of the switch when it should be. Now, in your case, since the R/H switch functions don't seem to be working, I would pick one of those functions and follow it from the ignition switch. Which wire from the ignition switch carrys the 12 volts to that function? Check it. Where does the wire go? Check that. It might be on the terminal board. Now check where the function comes from the terminal board. Check that. Then where does that wire go? Probably into the harness that goes to one of the switches on the R/H handlebar. Check that the 12 volts is there. That might meaning disassembling said switch or, less desireably probing the wire itself through the jacket with a sharp scribe. Still OK? Now does the 12 volts come out of the switch when switched? Check it. If yes, keep checking along the circuit path. If you don't get 12 volts when you should, you have to find out how the 12 volts is getting lost.

Maybe you want to use another approach other than the one I've described--and there are other ways to troubleshoot electrical problems. Whatever you do, use a methodical approach. Probing here and there and figuring out if 12 volts should be there, and if not why not, gets you thinking in circles and cussing the wiring diagram.

Or grab the advice from somebody else who might post about your problem. It doesn't matter too much. You just want to avoid scatter shooting the problem, checking things and then wondering what it means.


Ken

[sterob]

If I were you I would dis-connect all the wiring in the headlight and re-do them as neat as you can. it will take a couple of hours, but there is no substitute for neat wiring in a headlight shell. It will also help you with future wiring problems.
Is the wiring loom new? I bet not because they are very expensive ( used for only one year) I have a 74 R90S and I will be buying a new loom for it, not matter how good the other one is. ( They are 36 years old now,....lol)
Just MHO.....
Sterob

[George Ryals]

As you trace functions around the wiring, keep notes on what you checked and what you found.

It could be that one missplaced connection (or a not connected wire) is causing all of the problems. Tracing backwards on the diagram you may find that one switched hot wire og one ground is common to several of the problems.

Just checked my diagram of my '74 R90S... There are two bullet fuses on the circuit board inside the headlight bucket. One of them supplies switched 12 v to several of the idiot lights that are not working for you plus the license plate light.

[Major Softie]

I took his "smoke" comment to merely mean that the "magic smoke" that makes the system work was not getting everywhere it needs to go, not that it has escaped (burnt up).

I did not realize that Bosch systems were Smoke Control Technology - I thought that was a Lucas exclusive.

[Garnet]

I took his "smoke" comment to merely mean that the "magic smoke" that makes the system work was not getting everywhere it needs to go, not that it has escaped (burnt up).

I did not realize that Bosch systems were Smoke Control Technology - I thought that was a Lucas exclusive.

http://www3.telus.net/bc_triumph_registry/smoke.htm

[Ken in Oklahoma]

I did not realize that Bosch systems were Smoke Control Technology - I thought that was a Lucas exclusive.

I think you're right Major. I've never heard of smoke in connection with anything other than Lucas products. Certainly not Bosch. That's good news for DanielMC. He needn't concern himself about the presence or absence of smoke in the wiring of his decidedly Germanic R90S. Good old volts, amps, and ohms--and whether the damned thing works or not--is all he need concern himself with. That's got to give him a lot of relief.

Ken, smokeless in Oklahoma

[DanielMc]

Thanks guys for all the replies.

I have today checked all functions of the ignition switch and they seem fine. Over the next few days I'll take the advice offered and carefully re-install all the colour coded stuff on the circuit board - watch this space. I'm not too confident with electrics but the BMW system seems relatively idiot resistant if not totally foolproof.

Thanks for the advice about the smoke - I used to run British iron and always had a jar of Lucas replacement smoke in the workshop. Glad to hear that Bosch don't use it!

[Major Softie]

Thanks for the advice about the smoke - I used to run British iron and always had a jar of Lucas replacement smoke in the workshop. Glad to hear that Bosch don't use it!

Hey, those old original jars of Lucas smoke are becoming more and more rare. I'm sure you know you can get some serious money for that jar on eBay.

[SteveD]

When working in the headlight, I find this tool invaluable.

It's called a MacGills forcep. If you have any nurses or surgeons as mates....maybe a local tool shop has something similar.