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Bike Profile - Posted 28th January 2011

BMW K75RT Part 5 - Electrickery
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So far, his restoration of a 750 BMW has been relatively straightforward. But now Steve MacGregor encounters fear, loathing and electrics...

I like to think that I'm a reasonably intelligent person. I can fix most mechanical issues on my bike. I can strip and rebuild an engine. Sometimes these rebuilt engines even run.

So can you tell me why I am reduced to helpless incompetence when faced by electrical problems? If wiring diagrams featured Egyptian hieroglyphics, I couldn't understand them any less than I do now. This issue is compounded by the fact that the crisply lined diagrams never seem to bear anything more than a cursory resemblance to the rat's nest of wires and soggy insulating tape that lurks under the tank of most of my bikes.

Which brings me to the latest foible of my BMW K75. There I was, happy to have finally cured the misfire. The bike was parked outside the shed with the keys out and I was considering taking it for a ride. At that moment I became aware of an insistent 'tick, tock' sound. I looked at the bike. All four indicators were flashing.


The bike is fitted with a hazard warning switch, so I tried turning this off and on. No difference. I turned the ignition on and started the bike. All four indicators kept flashing. I tried the indicator switches. No change. I turned the ignition off and removed the key. No change. I disconnected the hazard warning switch. No change. The only way to stop the incessant flashing was to remove the indicator fuse. I tried replacing the fuse. 'Tick, tock, tick, tock.' I took the fuse out again and the flashing stopped.

It'll stop in a minute or two...

I had an electrical problem. I don't know of any other words that strike cold fear into my heart like these (except perhaps 'The dentist will see you now.'). As ever, I started optimistically. Perhaps it was just a loose connection? Except of course it never is, or at least I never find it. Once the tank was off, I could see swathes of wiring clinging to every frame tube like a noxious vine and disappearing into various mysterious black boxes.

I broke, cleaned and remade every connection I could see. When I replaced the fuse, the indicators continued to flash constantly. I did briefly try to read the wiring diagram, without notable success (see 'hieroglyphics' above). After that I tried the Net. Incidentally, whatever did we do before we could trawl the accumulated knowledge of the world via our computers? Asked people for advice I suppose. How quaint!

I found what appeared to be the answer on the Net. It appeared that I had a faulty indicator relay. I trawled eBay and quickly located one. A few days later, it plopped through the letter box. I fitted it and tentatively reinstalled the indicator fuse. No flashing. I started the bike. Still no flashing. Hurrah!

No, wait a minute, something isn't right here. When I pressed the right hand indicator switch, all four indicators flashed, but only for as long as I kept the switch pressed. When I released the switch, they went off. Likewise the left switch. Bugger! Is the replacement relay faulty? Do I have another problem? And, I now notice, the horn isn't working either. Aargh!

K75 bits on Right Now......

Generally what would be needed at this point would be calm, logical consideration of the problem. Except I know that this won't work with an electrical issue. Motorcycle electrical systems are powered by magic and fairy dust, so any attempt at an analytical approach is doomed to failure from the start.

A kindly friend, ground down by my constant whinging, pointed out that this is an ex-Police bike. So, perhaps it might be worth checking whether any of the additional wiring added by the police was causing the problem? This sounded like a good idea. The additional wiring added by the police was easy to identify - it didn't match the colours of the original loom and many of the connectors terminated in bare wire. Surely this can't be a good idea?

I carefully removed all the police wiring.

The indicators and horn still didn't work.

Hiding in the shed...

It was by sheer luck some time later that I noticed another blown fuse in the fusebox. This was odd, because I had checked the fuses when the indicator problem first arose, and all had been intact. The blown fuse was for, amongst other things, the horn. I replaced it and tried the horn. It worked. I happened also to try the indicators. To my surprise and joy, they also worked normally.

Now that I recall, I shorted out across a positive connection and earth when fitting the replacement flasher relay in the crowded relay box. This must have blown the horn fuse. I can only assume that blowing this fuse also had this strange side-effect on the indicators. Or that the Great Pixie that controls the electrics on my K75 had finally decreed that the indicators should work again.

One of the things that this problem forced me to confront was the sheer complexity of the electrics on this bike. There are a lot of wires under that tank and even the flasher relay has fourteen (yes, fourteen!) connections. However, this is the only electrical problem I have had whilst I have owned the bike, so perhaps it's not something I should be overly concerned about?

In fact, this is the only issue of any sort that I haven't directly inherited from a previous owner. Despite having done 55,000 miles in the last twenty years the K75 generally seems to be very reliable. Though of course, regular prayers to the Great Pixie can't hurt either…


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