Very Strange Electrical Problem...Any Ideas Appreciated

[Rotaxmaxracer]

Got a 2006 Servo ABS equipped GS12 that has been taken off the road for a while due to a problem with the dreaded Servo ABS. Decided to get her sorted, only then to find that my battery was dead and well past the point of being re-charged (zero output).

Replaced this with a Motobatt this week and went to connect her up in the normal way, but having connected the red leads first, nearly jumped through the garage roof with the spark generated when touching the black lead to the negative terminal. I immediately checked ignition was off, checked all of the leads and tried again...with exactly the same result (even with the engine kill switch switched to off).

This is above my remit, so had a good friend who is an electrical engineer in the Royal Air Force come over yesterday to take a look for me and equipped with his electrical meter and a wiring diagram, he set about trying to locate the fault.

Having removed the fuel tank for access, he went through the following tests for me and drew a bit of a blank...as follows:-

1. All battery earth leads checked for continuity to earth - all checked out OK
2. All battery positive cables checked for short to earth. All BAR the main power cable checked out OK. The main power cable shows a 3.6 Ohm impedance - is this normal, as he suspected this is why we had arcing/sparking?
3. Following the wiring diagram, he then went to try to eliminate potential faults on the main power circuit. Firstly he disconnected the starter motor - still showing 3.6 Ohm's - so eliminated this as the issue
4. Disconnected the alternator - still showing 3.6 Ohm's so that was not seemingly the problem
5. Disconnected the ABS Control unit - yet again, 3.6 Ohms showing, so no joy here
6. Finally, disconnected the starter relay as this was the last potential culprit on the circuit...yet again, still showing 3.6 Ohm's!!

He informs me that the only other independent unit on that circuit is the ECU, but didn't expect that to be the issue as there were no other indicated faults beforehand, prior to battery replacement.

He is asking if this 3.6 Ohm reading to earth is normal on a GS as he suspects not?

Outside of this, he says he can only imagine it to be a fault in the loom itself, which sounds like a nightmare to me.

Makes me wonder if this fault is what 'cooked' the old battery in fact?

If there is anyone familiar with the specific electronics who might offer any advice...I would really be most grateful

 

[JJH]

If your getting such a reaction on connecting the battery it's got to be a dead short somewhere in the circuit that is unprotected by a fuse. It's either a frayed wire (mice?) or the starter. Mobatts are a little taller is there any chance that the + terminal or wires are making contact with the frame or somehow earthing? JJH

 

[squibb34]

I know this sounds counter intuitive, but I did once purchase a replacement battery for the wife's Honda. Stupidly, I didnt look too closely at the terminal codings & just dropped it into the battery holder as a like for like swop - got similar symptoms to you. Turned out the batteries had been 'rationalsed' for the after-market range, so positive became negative, although they looked identical otherwise. So I had inadveratntly reversed the polarity - a few lead alterations soon sorted things.

Other than this, my first thought would be the starter circuit, but it seems like you have been there. Maybe you can get a guide to the level of current flow with an ammeter & then try pulling a few fuses, as none are blowing it seems. In my experience, I would start with any retrofit accessories - for instance Nav mounts are a well known problem area when the canbus keeps them permanently live due to current leakage.

Good luck .................... KEN

 

[Rotaxmaxracer]

If your getting such a reaction on connecting the battery it's got to be a dead short somewhere in the circuit that is unprotected by a fuse. It's either a frayed wire (mice?) or the starter. Mobatts are a little taller is there any chance that the + terminal or wires are making contact with the frame or somehow earthing? JJH

Thanks JJH, the battery terminals are clear and not touching, that much I can say. As for Mice, I don't know! The bike is parked right next to a plug socket with a hi-frequency rodent repellent device, so one would hope that would have put them off..but who knows?

Do you happen to know if the 3.6 OHM reading on the red power cable is acceptable - my friend seems to think this should be zero?

 

[Rotaxmaxracer]

I know this sounds counter intuitive, but I did once puchase a replacement battery for the wife's Honda. Stupidly, I didnt look too closely at the terminal codings & just dropped it into the battery holder as a like for like swop - got similar symptoms to you. Turned out the batteries had been 'rationalsed' for the after-market range, so positive became negative, although they looked identical otherwise. So I had inadveratntly reversed the polarity - a few lead alterations soon sorted things.

Other than this, my first thought would be the starter circuit, but it seems like you have been there. Maybe you can get a guide to the level of current flow with an ammeter & then try pulling a few fuses, as none are blowing it seems. In my experience, I would start with any retrofit accessories - for instance Nav mounts are a well known problem area when the canbus keeps them permanently live due to current leakage.


Good luck .................... KEN

Many thanks Ken...good advice. I will certainly point him in the direction of checking the ancillary items next

 

[Bendy toy]

Check the main battery lead (or a smaller non switched positive) has not chafed against the frame and welded itself in place. The main area tis happens is in the bundle alongside the battery and airbox.

 

[RoyF]

I would tend to agree with your mate, I wouldn't expect to see 3.6 ohms, as this means that there is a current draw of roughly 3.5 Amps from your fully charged battery, or around 43 Watts. Which there again doesn't sound like a direct short to me either, providing of course you've taken out of the equation the resistance of the actual meter leads....(Put the leads together, than take that reading from the reading you get from the bike).... If you've disconnected the starter and eliminated that, just a thought, do you have a factory alarm fitted?.... If the bike has been laid up for a while, could be a chance that your battery is recharging the alarm unit backup battery ?? ... Not got a circuit diagram to hand at the moment so that might be a load of tosh, but if you have an alarm try disconnectiong it.

Roy.

 

[*touring ted*]

Hi. I'm a BMW tech. Sounds like a dead short to me too.

Also do a polarity check on the battery or try another battery altogether. I'm still guessing on a short though.

Did the dealer change your ABS pump ??

Ive starter motors wired up backwards.

Sent from my G7-L01 using Tapatalk

 

[Rotaxmaxracer]

Hi. I'm a BMW tech. Sounds like a dead short to me too.

Also do a polarity check on the battery or try another battery altogether. I'm still guessing on a short though.

Did the dealer change your ABS pump ??

Ive starter motors wired up backwards.

Sent from my G7-L01 using Tapatalk

Thanks very much, the ABS pump is still the original - my plan was to get it to the dealer for a servoectomy once I had the bike running. Was running all OK before she went into dry dock for the past month, cannot understand why this might have occurred with it parked up?

 

[Rotaxmaxracer]

Thanks very much, sounds like an obvious and simple place to start!

 

[JJH]

Thanks JJH, the battery terminals are clear and not touching, that much I can say. As for Mice, I don't know! The bike is parked right next to a plug socket with a hi-frequency rodent repellent device, so one would hope that would have put them off..but who knows?

Do you happen to know if the 3.6 OHM reading on the red power cable is acceptable - my friend seems to think this should be zero?

Hi I'm not good enough to know exactly in £sp what exactly each component should read. The reaction your getting is clearly a major short however caused. I'm a more suck it and see person or what I usually do is post questions on here. JJH

 

[*touring ted*]

I would check the red cable from the battery live on its whole run.

Sent from my G7-L01 using Tapatalk

 

[davegs]

check your starter motor relay has not welded it's self together, and the bike in gear so when you connect the positive you will get a good spark
as your energising the starter motor which will take a high current.

 

[Gelandestrasse]

Any further with this? On my first GS (2004) I found various sites where looms running along the frame tended to rub and short through to the frame. As its loom-to-frame contact it's difficult to see unless you pull the looms around a bit. My issue was on the left hand side near the battery. The rear brake-light switch supply was shorted to earth, causing the brake light to stay on permanent and the ABS to trip out from start-up. It's a lottery which cable in the loom would be shorted, though, sounds like you have a permanent live....Symptom could be some green sulphate corrosion? When I got my second GS (2008) I snipped a few cable ties and put small bits of mouse mat between the loom and frame and then replaced the ties.

 

[Bendy toy]

I used some soft rubber sheet to do the same job. I also unpicked the main power lead to starter and sat it above the loom bundle. It takes up space and has no need to be within the main group.


Sent from my iPhone using Tapatalk

 

[davegs]

Well, what was the trouble?.

 

[Rotaxmaxracer]

Well, what was the trouble?.

After all of that...totally stumped!

My buddy came around yesterday and checked again. Still showing resistance on the live lead, he then set about stripping back the loom sheathing to check for faults in the wire. Nothing found...traced down to starter motor , alternator and just about everywhere else, but nothing found.

Spoke to a friend who is a GS whiz kid - who then said it was quite possible and in fact probable to have a small resistance due to the CanBus system. He suggested trying to connect the battery again to see what happened - red terminal first (naturally) and then review again.

With some trepidation we reconnected the battery and lo and behold...no sparks, no flashes at all???

After reconnecting all of the ancillaries / fuel tank and pump etc, we pressed the starter motor and she fired up straight away.

Really cannot understand it to be honest - so loom now re-wrapped, bike reassembled and hopefully all will now new OK.

Thanks for the help everyone, not sure what it was but just glad it appears now to be OK

 

[Delboy777]

It would be possible to have the battery the wrong way round if its a Motobatt, did you check that ?

 

[Rotaxmaxracer]

It would be possible to have the battery the wrong way round if its a Motobatt, did you check that ?

Yes, that would seem an obvious one wouldn't it..but no, battery defo fitted with the correct polarity

 

[Tractors are go]

Gremlins.