Hi Guys,

I took the MC21 out for a spin yesterday and after about 3 miles it died. Having got it home I found there is no spark, because the 15A ignition fuse has blown. I replaced the fuse and checked for a spark again but nothing. I then checked the new fuse, and that too has blown. I'm not too clued up on electrics so any suggestions would be greatly appreciated.

Cheers.
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definitly sounds like a short somewhere in the loom.

What does that fuse control? I think Andy has a wiring diagram in the workshop area of the site.

I would suggest you follow those wires that the fuse deals with and look for a cut wire, or a failing component on that fuse.
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Charles Gallant

Usual culprit is a chaffed loom, shorting a line to the frame somewhere. Gonna have to have a good look at everywhere the loom comes close to the frame...
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

There is a fool proof way of finding a short but you do have to be brave.

Replace the fuse with some wire and then look out for the where the smoke is coming from.
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If you dont like the way that i ride.....Stop trying to keep up!!!!!

Hey I tried the see where the smoke is coming from trick ones on my Volkswagon Rabbit! I wasn't chasing down a short, but I did accomplish the "Hey, look at all he smoke coming from the dash!" followed up with the "OH CRAP!!!, Pull the batter out!!!" dash. Ye, I did a hell of a job rebuilding that wiring harness under the dash on that car. Every thing still worked when I was done. Also learned a valuable lesson that day. When cutting wires? Cut one at a time, or pull the battery before cutting mutli wires at once
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Charles Gallant

Thanks for the suggestions guys. Don't think i'll go down the "look for smoke" route just yet. Knowing my luck it'll come from the PGM! Looks like my work is about to keep me away from the NSR for a few days but i'll keep you informed on what I find when I get a chance to investigate it further. In the meantime, if anyone has any more suggestions, keep them coming. Could it be the regulator/rectifier or a faulty kill switch? I've done a continuity test on the kill switch at the red 4 pin connector in the wiring box under the tank and it appears to be working.
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o o


Last edited by DifferentStrokes on Mon Sep 28, 2009 6:55 pm; edited 1 time in total

I had a similar problem and it was the brake light switch shorting on the forks after i had moved the lever to get a better riding position. The way i found it was to replace the fuse but before turning the ignition on pull apart all the connectors for the front loom which can be found just behind the head stock in the black box and then if the fuse does not blow replace them one at a time until the offending wires were found.
Best of Luck.
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MC21 300
Aprilia RS250 track bike

I've done a bit of investigating and have a bit more info, but still no cure:

I've had a good look at the loom and can't see any obvious earthing problems.

I've disconected the 4 pin connector for the kill switch/front brake switch and bridged the kill switch wires on the loom side and the fuse blows, so I guess the kill & brake switches are ok.

I then individually unplugged the Regulator, AC & pulse generators, power jet solenoids and oil pump solenoid and checked at each stage. The result is a growing pile of blown 15A fuses.

Then, with everything connected, I unplugged the black connector from the PGM3 unit as the black/white wire from the kill switch runs into it. I switched the ignition on and the fuse did NOT blow.

I may be barking up the wrong tree by assuming that the problem lies with the immediate kill switch circuit as this switch probably powers up half the loom.

Does this mean that the PGM is the problem, or does disconnecting the black connector simply break the circuit?

Sorry to be a pain, but i'm at the end of my tether
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fuses are blown due to more amps crossing the fuse then the fuse is designed to hold. In this case 15 amps. I would check the wiring with a multimeter and get the amp readings to get an idea what power is coming off the switch. From there back track the wiring and find out where the faulty component is.

What wires come into that fuse? what components are on those wires? Check all those components as well as whats behind those components.
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Charles Gallant

o o


Last edited by DifferentStrokes on Mon Sep 28, 2009 6:55 pm; edited 1 time in total

Very good point, hadn't thought of corrosion. Be careful fitting a higher rated fuse though, as the more current a cable draws the hotter it gets. Best solution is a multi meter evrery time.

Have you printed off the wiing diagram and traced through all the wires from the fuse that's blowing? Would help to eliminate all the stuff which isn't causing the problem...
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MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

I thought I had it sorted yesterday. I unplugged every component & terminal I could find, and re-connected them one at a time. The fuse blew when I connected the turn signal relay. I then fitted a new relay, switched the ignition on and all was well, but it wouldn't fire. I then noticed the electronic dash had gone out. I switched the ignition off for a few seconds then on again and the dash lights up but shows 8 volts and dropping, then goes out. The battery was showing 12.3 volts on the multimeter. If I switch the ignition on with the kill switch in the off position the dash shows the same voltage as the battery. Therefore, I only have a problem when the kill switch is in the run position.

One wire from the kill switch runs to the ignition fuse. Continuity seems fine and it is not earthing.

The other wire runs to the PGM (black connector), the power jet solenoids and the oil pump solenoid. I have isolated the solenoids which makes no difference, and when I unplug the black PGM connector, nothing powers up.

To top it all, when I plug in the old turn signal relay, the fuse does not blow now.

Looking at the wiring diagram, the circuit for the 15A ignition fuse runs through the lighting and auxillary fuses in the fuse box, which brings most of the loom into the equation.

My head hurts....
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