Possible Shorting Alternator

[Greasy Gilbert]

A while ago, I'm riding along and the bike cuts out.
Checking the bike over, I find that I have a total loss of electrical power. No RID, lights, horn, starter etc....nothing!
RAC guy comes, checks all the obvious things like fuses, loose wires and the like, then checks the battery and its as dead as a dodo.
He initially diagnoses it as a bad battery but when he connects his power pack, the thing arcs like crazy and he immediately suspects a shorting alternator ( he does this without going anywhere the alternator btw).

Now, I'm no auto electrician so bear with me while I ask a couple of dumb questions before I begin tearing the bike apart.

Does this sound like a credible diagnosis and has anyone had this happen to them?
I have a new battery on order, am I likely to damage the new battery by connecting it to the bike while I trace the fault?
Is there a way of isolating the alternator so that I can either confirm or discount his theory?

If any of this helps, it's a 2003 GS, bog standard, no extra lights etc.
It's fitted with a Denso alternator
I've had the bike for sixteen years and, since day one, the wiring around the headstock has had all the cable ties removed and at sometime in the past I've replaced the ignition switch harness when it failed. At present, all of this looks to be fine although I've yet to have a serious go at sorting it.

Any pointers would be greatly appreciated.

 

[Riceburner]

I've had the bike for sixteen years and, since day one, the wiring around the headstock has had all the cable ties removed and at sometime in the past I've replaced the ignition switch harness when it failed. At present, all of this looks to be fine although I've yet to have a serious go at sorting it.

Even removing the cable-ties isn't a sure-fire guarantee that the headstock issue won't happen. I had exactly that on one of my high-mile Rocksters, I took the cable-ties off when I bought it, and still had the wires breaking in the ignition loom after several years.

That would be my first thing to check for those symptoms.

 

[Neil W]

With mine it was the white plastic gubbins (electrical block) on the bottom of the ignition switch

 

[Paul Young]

Did the charging light come on?

 

[Greasy Gilbert]

Did the charging light come on?

No Paul, it didn't. Just cut out then all the electrics were dead.

 

[Neil W]

With mine I pulled up at a set of lights and it just died , everything went dead .
Tried the key a couple of times and nothing , lifted the seat to check the battery connections and fuses and everything was fine with no visible issues .
Waggled the wiring around the headstock and no difference , knew that would make to difference as the loom had been stripped back and rewound about 10 months previously .
Having had a similar issues with 1980's VW's that have a similar electrical connector block at the rear of the switch that fail due to the springs inside the unit loosing tension I tapped the bottom of the switch a few times and waggled the key and power was restored and I rode home .
I stripped the old unit and put in new springs from an old VW unit and it worked but just for peace of mind went out and bought a new unit (see second last page of the thread I started on Marrakesh red R1150GS )

Checked on the availability of the ignition switch (electrical part that plugs into the switch) part nos 61322306103 and it's three superseded replacement parts have been discontinued ,however, on checking up it turns out the part for the k1200 series (part nos 31322305742) is a direct fit with the exception of the cable being 80cms rather than the originals 40cms long.

Got the part from my local BMW dealer and it was cheaper by £5 than two large well known BMW parts specialists and it took all of 15 minutes to fit , hopefully no more embarrassing incidents and full service will be resumed

Is this the part you have replaced in the past ?

 

[Greasy Gilbert]

With mine I pulled up at a set of lights and it just died , everything went dead .
Tried the key a couple of times and nothing , lifted the seat to check the battery connections and fuses and everything was fine with no visible issues .
Waggled the wiring around the headstock and no difference , knew that would make to difference as the loom had been stripped back and rewound about 10 months previously .
Having had a similar issues with 1980's VW's that have a similar electrical connector block at the rear of the switch that fail due to the springs inside the unit loosing tension I tapped the bottom of the switch a few times and waggled the key and power was restored and I rode home .
I stripped the old unit and put in new springs from an old VW unit and it worked but just for peace of mind went out and bought a new unit (see second last page of the thread I started on Marrakesh red R1150GS )

Checked on the availability of the ignition switch (electrical part that plugs into the switch) part nos 61322306103 and it's three superseded replacement parts have been discontinued ,however, on checking up it turns out the part for the k1200 series (part nos 31322305742) is a direct fit with the exception of the cable being 80cms rather than the originals 40cms long.

Got the part from my local BMW dealer and it was cheaper by £5 than two large well known BMW parts specialists and it took all of 15 minutes to fit , hopefully no more embarrassing incidents and full service will be resumed

Is this the part you have replaced in the past ?

Cheers for that Neil.
Sounds very much like what happened to mine.
it's quite a while ago that I replaced it but I think that's the part. I changed mine because of an intermittent fault where sometimes the ignition would switch on ok, then other times wouldnt, rather than a total failiure.
Once the battery arrives and life gives me a minute, I'll have a look and see if that's where the problem lies.
In the meantime, thanks for your suggestions I'll report back.