Just a minor niggle, but one that I could use some advice on. I'm blowing a fuse!

A little background first, during my week down under, Rosskko generously lent me one of his Kollection (naked 1986 RT) so that I could get out and ride and enjoy some of the wonderful roads and Kompany hereabouts in New South Wales. 

Over the weekend, I was alerted to the fact that my tail light was not working and it was quickly discovered that the bulb was good but that No.2 fuse (7.5A) was blown. The bulb monitoring unit appears to be working correctly at start up, with the warning light clearing as soon as both brakes are operated and it was not detecting any faults with the tail light. The fuse was replaced and all appeared good, with the tail light (and brake lights) fully functional. The following day, as we continued the ride, Gaz noticed that my tail light was out again - we're not sure when it stopped working though. Quick check and Fuse No.2 had blown again. Rapidly depleting Gaz's supply of spare 7.5A fuses (the servo we stopped off at to avoid a monsoon didn't have any packs of fuses amongst their random selection of auto parts), the fuse was replaced and the tail light was working again. 

When I parked up near my hotel in Sydney late on Sunday afternoon , I noted that the tail light was still working. However, when I went to take the bike out for a spin (after work) on Monday, as soon as I turned on the ignition and lights - no tail light and fuse 2 had blown again. As a precaution, in case there were any strange voltage spikes, I ensured that the lights were switched off before starting the bike (I know that the load shed relay should cut the power to the lights anyway) and only switched them on once the bike was running. The (non standard K100) headlights and brake lights continue to work perfectly - it's just the tail light that goes. As it was still day light, I headed off on a planned run to West Head and managed to pick up a pack of spare fuses from a servo on the way. As the fuse pack did not have a 7.5A fuse, I inserted a 10A fuse and all good again, tail light working as it should. I rode back in the dark via Palm and Manly beaches, checking every now an again that I still had a tail light. Got back to the hotel and, bugger! No tail light again, 10A fuse blown. I have no idea when it actually went - somewhere between Manly and Sydney CBD. Incidentally, the speedo also stopped working during this short return leg - thank goodness for GPS speedo for keeping me honest. I think that is unconnected with the tail light issue (all other fuses are good) and may be due to a loose instrument cluster plug - I need to do a little more investigation into that issue.

I've looked at the electrical schematics and can't see any other load on fuse no2 apart from the tail light. The bulb monitoring unit is not picking up the failure and I am perplexed as to why Fuse no. 2 keeps on blowing. The tail light bulb appears good and works when it has power - I suppose it is possible that it has a breakdown to earth somewhere but I can't determine when the earth occurs as it appears to be a random event.

Any suggestions?

Born Again Eccentric wrote:
I've looked at the electrical schematics and can't see any other load on fuse no2 apart from the tail light.    Any suggestions?

Also check front park lamp bulb holder and the related wiring, as it's protected by the same fuse.
Check the wiring along the frame to the tail lamp, especially around the shockie mount.

G'day BAE, I think you are right that there is a short to earth either in the tail light fitting or in the wire itself. The cable insulation might have broken by chafing against the frame somewhere or wedged by a bolt/nut against the frame. Maybe follow the light harness from the rear and see if you can find any damaged cables. Also, have a look inside the electrics (relay) box to see if anything is untoward behind the fuse connections. Good luck. Cheers Tom

Thanks IngeK and Tom for the suggestions. I'll have a look to see what I can see wiring wise. 

As mentioned, it's a naked bike with non standard headlights and indicators (the tail cluster is original) - not sure if the parking light part of the circuit is connected. If I can't see anything obvious, I'll probably will change the tail light bulb anyway just in case there is an intermittent fault with the current one.



Might rig up a manual bulb monitoring unit too - something clagged on the backend that will reflect the light so I can see if/when it is working in my mirrors.

Paul, let me know if I can help. I'm staying in the CBD not far from. You've got my ph no. 
Unfortunately I didn't bring my dmm with me this trip.
I agree with the others. Likely to be the tail wiring as it goes over the top of the rear suspension. Also the custom h/light could mean the parking light wire is just hanging.
I doubt it's a component failure as it would likely blow straight away. It's an intermittent fault consistent with a loose wire shorting. 
Cheers

Kaptain Holister wrote:I agree with the others. Likely to be the tail wiring as it goes over the top of the rear suspension. Also the custom h/light could mean the parking light wire is just hanging.

I've not had the problem, so wouldn't presume to be definitive, but when a modification is made, I'd consider that area first.

It shouldn't be a hanging wire inside the headlight, as each of the two lights has a working parking light bulb (when the fuse isn't blown). It could be some issue related to the new headlights, though.

With a workshop full of tools in the tailpiece, its surprising there wasn't a DMM!  

Bill

Interesting to read here that Dai had the same problem as Paul on the same day.

Paul, Inge has advised why we didn't get a warning from the BMU.

Cheers

Yeah well, I haven't found the cause of mine blowing yet but I've stopped it from failing. I disconnected one spotlight. No, it doesn't make any sense. The spotlight has no sidelight!! and the entire aux headlight setup is a separate sub-loom. I get to do a bit more troubleshooting this weekend because the fuel tank has sprung a damn leak and has to come off for repair. Usual place - rear right.

Gaz80 wrote:Interesting to read here that Dai had the same problem as Paul on the same day.

Paul, Inge has advised why we didn't get a warning from the BMU.

Problem solved!

Thanks for the link Gaz - I hadn't spotted it in the new posts - however, I had come to the same conclusion as IngeK that the blowing fuse removed power from the BMU and therefore the tail light failure went undetected by the BMU.

Inge was also right about the probable fault being trapped wiring (but not by the rear shock). Top marks to Tom, Indian and Kaptain too - for highlighting the probable problem area.

After work today, I had a quick look in the vicinity of the rear shock, but nothing obviously wrong. As I was limited in day light hours and wanted to get out for a ride down to Scarborough, via the twisty road through the Royal National Park and Sea Cliff Bridge, I put in a new fuse (15A this time) and tail light was observed to be working.

I set off into some horrendous Sydney southbound "rush hour" traffic and by the time I turned off the main road onto the road through the park it was already dusk. This would be a cracking good ride in daylight! Due to the darkness, I was able to see the glow of the tail light reflected off the tarmac, so knew that all was good. When I got to my destination, as I turned the bike, I noticed that the tail light had gone out again. Fuse 2 blown again. I inserted my next smallest fuse - a meaty 25A one, reasonably confident that there was no sensitive electronics in the circuit that would be damaged. Tail light back on and remained on all the way back to the hotel (about 80km). As I parked up in the secure parking, I happened to turn the steering to full right lock. Briefly the BMU lit up and then, with an audible "pop" the fuse blew and the tail light went out, as did the BMU warning light. I immediately replaced the fuse with yet another spare (I had bought a couple of extra packets of assorted fuses on my way back from my ride) and turned the steering to full left lock and then to full right lock - as soon as I got to right lock,"pop" and fuse blown again. This left me in no doubt where the problem lay. Inge K was right again, the parking light wiring was the culprit. I had already determined that the twin headlight set up did utilise the parking light circuit. A minute or so later, I was able to identify where the fault was - the yellow wire leading to the parking light was trapped against the lower fork clamp and was crushed every time the steering was turned to the right. Over time, the insulation had split to expose live wires. As the steering was turned to full right lock, the live wires earthed against the fork clamp and blew the fuse. 

I tried to get a pic of the wire in situ, but it came out too blurry, so I can only offer a pic of the offending wire once removed from the clutches of the lower fork clamp


By putting in a 25A fuse, it had meant that under the direct earth condition, the fault occurred for a few milliseconds longer before the meatier fuse blew - this was sufficient time for the BMU to detect the fault briefly before clearing as the power source was removed. It was then a simple matter of pulling the wires up out of harms way and wrapping them in some self amalgamating tape to restore some insulation.

Incidentally, speedo was working again after tightening up the instrument cluster plug...but not sure that the fan is cutting in as I got a red high temp light while stuck in the rush hour traffic - cleared as soon as I was moving again and had air flow over the radiator.

Thanks to all that contributed to finding the problem area.

No point in wasting time the 25A fuses , just go straight to old bent nail instead of a fuse and see where the smoke starts coming from

If you'd done it after dark , you'd have seen the sparks from the fork leg and the glowing wire !!